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On Multi-Classifier Systems for Network Anomaly Detection and Features Selection

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On Multi-Classifier Systems for Network Anomaly Detection and Features Selection Powered By Docstoc
					                                                               (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                         Vol. 8, No. 2, 2010

   On Multi-Classifier Systems for Network Anomaly
           Detection and Features Selection

          Munif M. Jazzer                                  Mahmoud Jazzar                                          Aman Jantan
         Faculty of ITC,                              Dept. of Computer Science                           School of Computer Sciences
   Arab Open University-Kuwait                            Birzeit University                             University of Science Malaysia
            Kuwait.                                       Birzeit, Palestine                                 Pulau Pinang, Malaysia


Abstract—Due to the irrelevant patterns and noise of network                    In this paper, we have used fuzzy cognitive maps (FCM) [4,
data, most of network intrusion detection sensors suffer from the           5] to express the causal relation of data and calculate the
false alerts which the sensors produce. This condition gets worse           severity and relevance to attacks or normal connection. We
when deploying intrusion detection measures in real-time                    have also used the SOM method [6] to help us evaluate the
environment. In addition, most of the existing IDS sensors                  related data patterns and attributes. As a result, benign concepts
consider all network packets features. Using all packets features           can be dropped or ignored and other can be addressed as a
for network intrusion detection will result in lengthy and                  potential risk of attacks or error caused.
contaminated intrusion detection. In this research we highlight
the necessity of using important features in various anomaly                     The main objective of this paper is to present a new multi-
detection cases. The paper presents a new multi-classifier system           classifier system based on causal knowledge acquisition and
for intrusion detection. The basic idea is to quantify the causal           show its effectiveness for anomaly detection. Features selection
inference relation to attacks and attacks free data to determine            measures are also considered and illustrated in various
the attack detection and the severity of odd packets. Initially, we         detection cases. The detailed system process overview is
have refined the data patterns and attributes to classify the               illustrated in Fig. 3. A brief summary of the exploration
training data and then we have used the SOM clustering method               modules and its processes details are available in Table II. The
and the fuzzy cognitive maps diagnosis to replicate attacks and             rest of the paper is organized as follows: Anomaly detection in
normal network connection. Experimental results shows that the
                                                                            network-based IDS and related issues are discussed in section
classifiers gives better representation of normal and attack
                                                                            II, the related works are discussed in section VI, the classifiers
connection using significant features.
                                                                            detection process in section III, and the features selection
   Keywords- Anomaly Detection; SOM; FCM; Security                          process in section IV. Section V describes the performance
                                                                            evaluation, related discussion, concluding remakes and future
                                                                            work.
                       I.    INTRODUCTION
    The basic function of anomaly-based sensors is to detect                                  II.   ANOMALY DETECTION
any deviation from normal system behavior. However, clear
merits between normal and abnormal patterns are very difficult                  A typical anomaly-based detection system works on the
to realize in practice especially when new systems are added or             notion that abnormal behaviors and activities are different
removed from the system network [1, 2]. As a solution, we are               enough from normal (legitimate) behaviors profile.
trying to tackle this problem by implementing unsupervised                      In anomaly detection, patterns are analyzed based on some
learning and knowledge discovery techniques such that there is              measures (statistical, threshold, rule-based ...) to determine the
no need for training the system on clean data.                              events or activities that are malicious or abnormal. The most
    The typical network-based IDS process system activities                 attractive thing here is that the IDS that employ these kinds of
based on network data and make a decision to evaluate the                   detection mechanisms have abilities to detect symptoms of
probability of action of these data to decide whether these                 attacks without previous knowledge of their attack details
activities are normal or intrusions [1]. In order to evaluate the           which makes them ideal for detecting the newly rising attacks
system activity and trace the probability of action of normal vs.           signatures [7]. Furthermore, information produced by anomaly-
intrusive data, the basic knowledge of network attacks is                   based detection systems can be used to define signatures for
necessary. The problem is that network attacks may not happen               misuse-based detection systems. On the other hand, the output
at single action such that one massive attack may start by                  produced from anomaly-based detectors can be in turn used as
seemingly innocuous or by small probe action to take place [3].             information source for misuse-based detectors i.e. to double
Such situation articulates the need for a defense-in-depth                  check for legitimate activities that might be intrusion [8]. As
strategy. At this point, we have considered the domain                      result, anomaly detectors are attractive and can play a measure
knowledge of network data, thus we need to extract the causal               part in the future IDS. A block diagram of a typical anomaly
relation of these data and make inference with it. First, we                detection system is shown in Figure 1.
cleanse the data and then diagnose the clean data patterns.




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                                                                                                      ISSN 1947-5500
                                                                              (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                        Vol. 8, No. 2, 2010
                     Update profile                                                     A. Preprocessor Module
                                                     Statistically
                                                                                             Data preprocessing module performs the final preparation
                                                                     Attack             of the target data records. This includes the slicing of the large
 Audit Data                  System Profile                          State
                                                                                        dataset. The selection criteria based on pre-user defined
                                                      Deviant?                          mechanisms or threshold value, and the number of the starting
                 Generate new profiles dynamically                                      row in the given dataset. First, we introduce the input file with
                                                                                        all the input vectors then we put the number of vectors required
                 Figure 1.         A typical anomaly IDS [7].                           to read, the number of levels and the threshold value. In this
                                                                                        module, the user can introduce the number of neurons and the
    The main issues with the anomaly-based detectors are that                           selected features which will be used in each SOM level. After
they produce high number of false alerts [7]. According to [9],                         that, the user can train and save the neurons state accordingly
anomaly detectors are tending to be computationally expensive.                          for each training level. The elapse time is the difference
This is because there are several metrics which are often                               between the first and the last level according to the user
maintained and often need to be updated against every system                            predefined number of levels.
activity; and they might be gradually trained incorrectly to
recognize abnormal behaviors as normal in the long run due to
the insufficient data.
                                                                                                                       SLICING
    In this study, we have assumed that the neural networks
behaviors in SOM will learn patterns of the normal system
behavior and continually produce profiles to incorporate with                                                         READING
the fuzzy logic behaviors in the FCM. This is also to determine
the appropriate membership function which will help in                                   KDD’99
reducing false alerts and increasing the detection accuracy of                           Dataset                     SELECTION
the detection sensor [10].                                                                                                                           Target Data
                                                                                                                    User         Threshold
          III.     THE CLASSIFIER INTRUSION DETECTION                                                              Defined

    The ability of detecting/preventing new attacks without
prior knowledge of the attack behavior is a tough task,                                                P R E P R O C E S S I N G
especially the way of determining the input features to monitor
normal versus intrusive behavior. For this challenging task, we                                        Figure 2.             Preprocessing module.
decide on unsupervised learning techniques as they are the best
suited for such situation [27].                                                              This module involves slicing the dataset into five classes.
                                                                                        Each class symbolic-valued features are mapped into numeric-
    The focus here is to provide a multi-classifier system which                        valued features. Symbolic features such as protocol type
can work as an inference engine supplement for enhancement                              symbols (TCP, UDP, and ICMP) were mapped into integer
of the IDS capability. Using the classifiers system, we can                             values. More details about the data used and the data classes
determine the importance of features in various anomaly                                 are available in section V. Each symbol data is corresponded to
detection cases.                                                                        a position in the labels array and this position will be used to
    In order to build the inference engine classifiers system, we                       fill the input vector. In this module, we have focused on the
have used the unsupervised learning method so-called                                    final preparation of the target data to be presented to the
Kohonen’s maps (SOM) [6] for clustering and recognition of                              subsequent module.
input data and the fuzzy cognitive maps (FCM) [5] to detect                                 The prime importance of this module join up by the fact
features relevancy. The FCM use causal reasoning to assess the                          that finding or discovering related patterns in a data set is an
SOM output and then model the final decision. FCM are ideal                             instructive process, with slight or even no former knowledge
causal knowledge acquiring tool with fuzzy signed graphs                                about the structure of the given dataset to be examined [21].
which can be presented as an associative single layer neural                            Hence, dependence on clean dataset can give more confidence
network [4]. Using FCM, our methodology attempt to diagnose                             that the assumption drawn from the pattern exploration output
and direct network traffic data based on its relevance to attack                        can be treated as being precise to the model of the data being
or normal connections.                                                                  examined. Moreover, the redundant and non related patterns
    By quantifying the causal inference process we can                                  can be dropped earlier to avoid congestion on the subsequent
determine the attack detection and the severity of odd packets.                         operations. Thus, it gives the system vigilant and the flexibility
As such, packets with low causal relations to attacks can be                            of features selection for further exploration of attacks details.
dropped or ignored and/or packets with high causal relations to
attacks are to be highlighted. In the following subsections, we                         B. Data Mining Module
elaborate the classifiers system modules. Figure 3 shows the                                Data mining module is the first important component of the
overall detection process.                                                              classifiers system. The task of this module is to generate cluster
                                                                                        information such that generates logical and homogeneous
                                                                                        clusters from the input dataset. To achieve that task, a network




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                                                                                                                     ISSN 1947-5500
                                                                       (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                 Vol. 8, No. 2, 2010
classifier (SOM) is used to do an initial recognition of the                                 h ci ( t ) = h ( rc − ri , t ) ∝ ( t )                   (2)
network traffic flow to detect abnormal behaviors. To achieve
the key objective of the data mining module, the data is first
passed through the SOM such that the data and its relevant
features are represented by the SOM. The learnt SOM then                             Where: rc is the location of the winner unit; ri is the
passed through the fine tuning module for knowledge                               location of the unit i on the grid map and ∝ (t ) is the learning
discovery using the FCM exploration.                                              rate factor over minimum time t interval. At this stage the map
    Two stages are required in order to create the SOM which                      converge to an inactive stage which approximates the
are the initialization and the training of the SOM. The                           probability density function of the high dimensional input data.
initialization process sets up the map with the desired                           The learning rate and the neighborhood proceed by time until
dimensions and initial weights for each unit of the map. The                      convergence. Once the maps are trained, usually the concept of
training process allows the map to adapt to the features of the                   BMU which is used to facilitate the labeling of the consequent
data set during a number of epochs.                                               levels of fine tuning and refinement for the sake of tracing the
                                                                                  related and diverse patterns.
    At each epoch one input vector x is compared to all
neurons weights w with a distance function (Euclidean or                              The objective of the SOM visualization component is to
Manhattan) to identify the most similar nodes so-called the best                  render the SOM text file to a graphical representation. In SOM
matching unit (BMU). Once the BMU has been found, the                             cluster files, the problem arose with neighboring neurons which
neighboring neurons and the BMU itself are updated according                      are out of clusters and did not reflect exactly the severity of
to the following rule:                                                            attack-ness in network connections [9]. That is because a
                                                                                  network attack may not happen at a single action such that one
     wi (t + 1) = wi (t ) + hci (t )[ x(t ) − wi (t )]           (1)              massive attack may be start by seemingly innocuous or by
                                                                                  small probe actions to take place [3]. In SOM classification
                                                                                  process per example in [28], a genetic or clustering algorithm
  Where: t is an integer which denotes time, hci (t ) is the                      was used at certain attack zone to classify each attack by class
neighborhood function around the winner unit c and x(t ) is                       whereas suspicious neurons which near the attack zone or out
                                                                                  of the cluster area are not analyzed and remain suspicious were
the input vector drawn at time t. By updating the BMU and                         they might be benign. As one potential solution to this problem
other units in the neighborhood, the distance between the                         in the hierarchical SOM [2], they consider the potential of
BMU and the neighbors are brought closer together. The                            studying the domain knowledge of features to be applied to the
neighborhood function consists of two parts, one that define                      whole SOM concepts.
the form of the neighborhood and the other is the learning rate.

                                                                Causal Knowledge Discovery (Exploration)




                                                                                                      FCM Exploration Module
                   Preprocessing Module                                     Data Mining
                   (Data Mining and Knowledge
                         Discovery Steps)                                     Module
                                                                                                            Pattern            Hypothesis
                                                                        •     SOM Training                 definition          formulation
              DATA       Preprocessing                Pattern           •     SOM
                                                                              Clustering
                                                                        •     Inference                    Selection            Exploration
                                           Target
                                            Data


                                                                  Visual               Odd               Evaluation /            Knowledge
                                                                Exploration           Patterns          Interpretation


                                                                                                        Reduced odd patterns

                                         Figure 3. The classifiers anomaly detection system.

   To increase the correlation among the neurons in the                              In this study, we suggest an improvement to this process by
produced map grid, we minimize the neighborhood function                          considering the domain knowledge of particular neurons (odd
and the learning rate by considering the minimum time                             neurons). Therefore, we used the FCM to calculate the
interval according to the following rule:                                         severity/relevance of odd concepts (neurons) to attacks. Thus,




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                                                                                                               ISSN 1947-5500
                                                              (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                        Vol. 8, No. 2, 2010
benign concepts can be dropped and/or others can be addressed             and value trace are calculated according to [29]. The estimated
as a potential risk of error caused.                                      the total degree of abnormality and attack detection per packet
                                                                          are considered according the following rule:
C. FCM Exploration Module                                                                     n
    The multi-classifier intrusion detection model is a defense-               Un ( x ) =   ∑i =1
                                                                                                    Ei                                     (3)
in-depth network based intrusion detection scheme. The model
utilizes the domain knowledge of network data to analyze the                   Where:        Un(x) : Abnormality per packet
packet information. Based on the analysis given, benign
packets are dropped or blocked and high risk packets are to be
                                                                                             Ei : Effect value of packet
highlighted or blocked using a causal knowledge reason in                                    n : Total feature number of abnormality
FCM.
    The flowchart of the overall exploration steps are further                                             Pattern Definition
illustrated in Figure 4. In this module the received data
attributes will be carried out for fine-tuning in the FCM                                                Hypothesis Formulation
framework. As such, the neurons which represent low effect or
less correlated to other attack like neurons are dropped or
ignored and the high suspicious nodes are to be highlighted.                                          Exploration and Selection
Table I shows the degree of the effect and the value trace which
represent the relations between neurons.
                                                                                                              Evaluation

        TABLE I.      EFFECT AND RELATION VALUE TRACE
                                                                                                     Odd Pattern Reduction and
                      Effect                  Value Trace                                             Knowledge Discovery
                      Normal                       0
                      Slight                      0.2
                       Low                        0.4                                Figure 4. The knowledge discovery module steps.
                     Somehow                      0.6
                       Much                       0.8                        Once the abnormalities per un-clustered packets are
                       High                        1                      calculated, the low malicious packets are dropped or ignored
                                                                          and the rest are considered as concepts in the FCM. It is now
    Initializing the FCM includes the definition of the FCM               important to measure the effect/influence value among the
concepts and building the relations among these concepts by               suspicious concepts to determine the path of the existing or
building a global matrix [4, 5]. However, in order to build that          ongoing attack. If the effect value is zero then there is no
matrix we have defined the weight of odd neurons according to
                                                                          relationship among these concepts. Figure 5 illustrates the
the total effect factor Un (x ) and the grade of causality W ij
                                                                          FCM algorithm.
between the nodes Ci and C j           according to the following
assumptions:                                                                Algorithm   FCM

                                                       { }
                                                                            Inputs      SOM alerts, data patterns
   1.    If C i ≠ C j and E ij 〉 0 then Wij + = max E ij
                                                       t
                                                                            Outputs     Reduced alerts, Replicate attack and normal
                                                  = max{E }
   2.    If C i ≠ C j and E ij 〈 0 then Wij   −           t                             connections
                                                         ij                 Method
   3. If C i ≠ C j then E ij = 0 and W ij is zero                              1   Define the number of odd neurons (SOM Alerts)
                                                                               2   Define the number of concepts derived from data
                                                                                   patterns
    Each feature parameter of odd neurons is measured based                    3   Call FCM initialization
on a comparison criteria to detect the interrelation between                   4   Calculate the abnormality per neuron
neurons i.e. determine the attack detection. To calculate the                  5   Drop neurons if the abnormality is low
abnormality factor per packet we need to estimate the effect                   6   Until convergence show the link of related factors
value of each feature parameter. The total degree of                        End
abnormality of odd neurons is calculated according to the total                                   Figure 5. FCM algorithm.
effect factor, the evaluation criteria illustrated in section IV.
     The task of FCM is to determine the causal relationship                 Once the normal and abnormal (attacks) data are replicated
between the suspicious or odd neurons noted by SOM to                     then it is time to explore the causal relationship of attack and
quantify causal inference process. By quantifying the causal              alerts data to settle on the related factors and concepts. By
inference process we can determine the attack detection and the           doing so, we can further increase the detection accuracy and
severity of odd neurons such that neurons with low causal                 discover more related factors effectively. The knowledge
relations to be dropped or ignored. Using factors, rules and              discovery steps are illustrated in Figure 6.
effect values we can estimate the total degree of effect value
and hence the abnormality per packet. The effect parameters




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                                                                                                         ISSN 1947-5500
                                                                             (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                       Vol. 8, No. 2, 2010
                                                                                        16       num_root                                    continuous
  1     Define attack and alerts patterns                                               17       num_file_creations                          continuous
  2     Select atterns with probability P                                               18       num_shells                                  continuous
  3     Pick concepts with related similarity measures                                  19       num_access_files                            continuous
  4     Test correlations                                                               20       num_outbound_cmds                           continuous
  5     Drop benign concepts (low correlation measures)                                 21       is_hot_login                                discrete
  6     Highlight the rest as an attack or major error                                  22       is_guest_login                              discrete

                                                                                                        TABLE V.      TIME-BASED FEATURES
                        Figure 6. Exploration steps.                                    # No     Feature name                                       Type
                                                                                        23       count                                       continuous
  Table II gives a brief summary of the framework modules                               24       serror_rate                                 continuous
and its processes details.                                                              25       rerror_rate                                 continuous
                                                                                        26       same_srv_rate                               continuous
         TABLE II.        EXPLORAION MODULES SUMMARY                                    27       diff_srv_rate                               continuous
                                                                                        28       srv_count                                   continuous
                                                                                        29       srv_serror_rate                             continuous
      Module             Tasks          Method         Input     Output
                                                                                        30       srv_rerror_rate                             continuous
                                                                                        31       srv_diff_host_rate                          continuous
                                      Standard                                          32       Dst_host_count                              continuous
                                                                Cleansed
                     Data             and raw          Data
 Preprocessing                                                  and                     33       Dst_host_srv_count                          continuous
                     preprocessing    data             file
                                                                processed               34       Dst_host_same_srv_rate                      continuous
                                      selection
                                                                data file               35       Dst_host_diff_srv_rate                      continuous
                                      Cluster          Data     Report                  36       Dst_host_same_src_port_rate                 continuous
 Data Mining         Data mining
                                      analysis         file     data files              37       Dst_host_srv_diff_host_rate                 continuous
                                                       Data                             38       Dst_host_serror_rate                        continuous
                     Pattern                           files,   Report                  39       Dst_host_srv_serror_rate                    continuous
 Exploration                          Exploration
                     Discovery                         SOM      data files              40       Dst_host_rerror_rate                        continuous
                                                       files
                                                                                        41       Dst_host_srv_rerror_rate                    continuous

                                                                                           A typical anomaly-based detection system works on the
               IV.   THE FEATURE SELECTION PROCESS                                     notion that abnormal behaviors and activities are different
                                                                                       enough from normal (legitimate) behaviors profile. Once the
    There are 41 features defined for every connection record.                         normal and abnormal (attacks) data are replicated then it is time
A complete listing of the sets of features defined for the                             to explore the causal relationship of attack and alerts data to
connection records is given in the three tables below. The                             settle on the related factors and concepts. By doing so, we can
tables contain the list of 41 features available in the KDD’99                         further increase the detection accuracy and discover more
dataset [30]. These features are the intrusion detection dataset                       related factors effectively. Our approach here is to study the
variables which are used for most of the IDS development and                           probability of action of odd patterns and check for their
testing environment.                                                                   correlation such that the higher correlation the higher related
                                                                                       factors. The comparison criteria take the values between 0 and
        TABLE III.       BASIC FEATURES OF INDIVIDUAL TCP
                                                                                       1 such that:
                            CONNECTIONS
                                                                                               If X and Y are two different concepts then:
 # No    Feature name                                      Type                                Prob(X) = P(x)                                               (4)
 1       duration                                          continuous                          Prob(Y) = P(y) * S                                           (5)
 2       protocol_type                                     discrete
 3       service                                           discrete
 4       src_bytes                                         continuous
                                                                                         Where: S is the similarity ratio between X and Y. The
 5       dst_bytes                                         continuous                  concepts were defined according to the similarity ratio
 6       flag                                              discrete                    according to the following assumptions:
 7       land                                              discrete
 8       wrong_fragment                                    continuous
                                                                                                               If X = Y then S = 1
 9       urgent                                            continuous
                                                                                                                  If X <> Y then
                TABLE IV.        CONNECTION FEATURES
                                                                                                                       S=0
                                                                                          In other words, certain alerts can be assumed as an attack if
 # No    Feature name                                      Type                        they have similar probability of action. The similarity factor
 10      hot                                               continuous
 11      num_failed_logins                                 continuous
                                                                                       can be calculated according to the following rule:


                                                                                                    {
 12      logged_in                                         discrete
 13      num_compromised                                   continuous                                1X =Si
 14      root_shell                                        discrete                          Sf =    0 X ≠ Si                                         (6)
 15      su_attempted                                      discrete




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                                                                                                                    ISSN 1947-5500
                                                                          (IJCSIS) International Journal of Computer Science and Information Security,
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  Where: S i is a feature of set S and X is a comparison. The                              V. PERFORMANCE EVALUATION AND DISCUSSION
availability of features was estimated according to the                                 The proposed classifiers system architecture is two layers
following rule:                                                                     system architecture. The SOM layer trained to cluster the input
                                                                                    data for each connection type. The layer of the SOM is

          {
                                                                                    belonging to one of the five classes of the dataset and will
              1X ∈S                                                                 provide an output relevant to specific class. The second layer is
   Af =       0 X ∉S                                             (7)                the FCM framework. This layer uses a causal reasoning to
                                                                                    measure the severity of odd neurons (SOM alerts). The main
   Where: S is the set of features and X is a comparison. In this                   advantage here is to call attention to how domain knowledge of
                                                                                    neurons (network packets) can contribute on tracing new
study, we have used the same testing data procedures as in
                                                                                    attacks or find path of on-going or existing attacks.
(DARPA, 1998 and 1999) [30, 31]. We have extended that
into evaluating the online generated (dumped) data patterns                             In this study, we have used the most popular IDS evaluation
from CS USM computer forensic research lab as well as                               data in which most of researchers aware of and used for
considering data features optimization and selection for a                          evaluating their research, the KDD Cup 1999 intrusion
                                                                                    detection contest data [30] followed by the success of the 1998
comprehensive evaluation as shown in the evaluation criteria
                                                                                    DARPA Intrusion Detection Evaluation Program by MIT
diagram in Figure 7.                                                                Lincoln Labs (MIT Lincoln Laboratory) [31]. Table VI gives a
                                                                                    sample distribution of the KDD’99 datasets.
                        %False           Detection
                        Positives          Rate                                         TABLE VI.      SAMPLE DISTRIBUTION OF KDD’99 DATASET

                                                                                     Dataset Name     Normal   DOS     Probe     U2R      R2L       Total
                              Evaluation                                              Whole KDD        19.8    79.3     0.84     0.001    0.02   4,898,430
       DARPA 1998 and
            1999               ABC of                  Online Data
                                                                                      10% KDD          19.79   79.2     0.8       0.01     0.2   494,020
     •   10%                    IDS’s                                                Corrected Test    19.58   73.9     1.3       0.02     5.2   311,029
                                                  Filter             Slicer
     •   Corrected
     •   Whole KDD
                                                           Sniffer
                                                                                      The dataset contain 41 attributes for each connection record
                              Feature Selection                                     plus one class label and 24 attack types which fall into four
                                Procedures                                          main attack categories [32] as follows:
                          •     Combinations
                          •     Optimization                                            1.    Probing: surveillance attack categories
                                                                                        2.    DoS: denial of service
                                                                                        3.    R2L: unauthorized access from a remote machine
                   Figure 7. IDS evaluation ABC.
                                                                                        4.    U2R: unauthorized access to local super user (root)
    In Figure 7, we have highlighted the most typical                                         privileges
evaluation ABC for any IDS technology. It is also important to
mention that there are many issues available regarding these                            The dataset was established to evaluate the false alarm rate
evaluation ABC but we disregard to testing environment issues                       and the detection rate using the available set of known and
as the research mainly focus on the development of the                              unknown attacks embedded in the data set [33]. We have
inference engine components i.e. the multi-classifier system.                       selected subsets from the so-called corrected.gz, 10% KDD,
Moreover, we have considered very important issue here which                        and the whole KDD files for testing purpose.
is the data feature selection procedure. The reason is due to the                       The selected subsets contain records with non zero values
fact that most of the existing IDS technologies use all or none                     because some attacks are represented with few examples and
systematic patterns of data attributes to discover known or                         the attack distribution in the large data set is unbalanced.
unknown intrusive activities; which will result in a lengthy                        Considering the whole data set degrades the IDS performance
intrusion detection process or even degrade the evaluation                          evaluation and result in boredom and lengthy detection process.
criteria of the IDS [26].                                                           However, the collection, preprocessing and calculation of false
    As stated earlier, the suggested approach is anomaly-based                      and true alert of test data are followed as in [3] according to the
on causal knowledge reasoning. Using FCM, we attempts to                            following assumptions:
diagnose and direct network traffic data based on relevancy to                               FP: the total number of normal records that are
attacks and attack free connections. The SOM-FCM approach                                        classified anomalous
is a defense-in-depth intrusion detection model which utilizes                               FN: the total number of anomalous records that are
the domain knowledge of network data to analyze packet
                                                                                                 classified as normal
information. The SOM and FCM schemes in combination and
                                                                                             TN: the total number of normal records
in isolation can be further modeled as an inference engine
component for anomaly intrusion detection.                                                   TA: the total number of attack records
                                                                                             Detection Rate = [(TA-FN)/TA] * 100
                                                                                             False Alarm Rate = [FP/TN] * 100




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                                                                                                               ISSN 1947-5500
                                                                   (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                             Vol. 8, No. 2, 2010
  In all cases, we run our experiment on a system with 2.667                  TABLE X.        EXPERIMENTAL RESULTS FROM SOM-FCM USING 10% KDD
                                                                                                            DATA
GHz Pentium4 Processor 506 and 256MB PC3200 DDR400
RAM Running Windows XP.                                                                                                    # Detection Records
                                                                                                            Normal
   For comprehensive evaluation, the performance measures                        Feature         #                        FP       FN
                                                                                                             Rate                          Detection
                                                                                   Set        Records                    rate     rate
of SOM, FCM and the combination of SOM-FCM are tested                                                        (%)                           Rate (%)
with specific and all features populations. As we have learned                                                           (%)      (%)
                                                                               Connection     494,020         19.79     0.033     000         100
from the initial population testing, the dataset in 10% KDD
                                                                                 Content      494,020         19.79     0.002     000         100
simulates the entire or whole KDD. Therefore, we have                             Time        494,020         19.79     0.001     000         100
conducted the test with only 10%KDD and the so-called                          All Features   494,020         19.79     18.07     000         100
CorrectedTest data.                                                                           Overall                   4.52      000         100
    Initially, we have considered the feature selection based on
content, time and connection features for comprehensive                          All of the above mentioned features and partitions of
experiments as shown in the following tables. First, we have                 features illustrated in Section V have been applied to the inputs
tested the SOM and FCM in isolation and then the combined                    of the SOM, FCM, and SOM-FCM using single and multiple
SOM-FCM approach. From the obtained results we have                          SOM classifiers. Initially, these methods are assumed to work
noticed that there is a prime importance for the connection                  as single class detectors for the input data patterns. As
features for detecting various attacks such that they can help in            mentioned earlier, the SOM-FCM is a defense-in-depth
reduces false positives in most of the cases.                                anomaly intrusion detection scheme. For classification purpose,
                                                                             the classifiers parameters should be trained according to the
                                                                             nature of the given training data and then used to classify and
TABLE VII.       EXPERIMENTAL RESULTS FROM SOM MULTIPLE LAYERS USING         categorize the data.
                         CORRECTED TEST DATA

                                           # Detection Records
                                                                                 Since we employ the SOM classifier for each attack class
                             Normal                                          category at the first layer of the SOM-FCM intrusion detection
    Feature          #                   FP     FN
                              Rate                      Detection            model, the number of SOM classifiers can be manipulated for
      Set         Records               rate    rate
                              (%)                       Rate (%)             testing purpose. Then the classifiers system can work as
                                        (%)     (%)                          signature based classifiers system and each classifier work as
  Connection      311,029      19.58    15.7    0.002     99.3
    Content       311,029      19.58    27.45    000       100
                                                                             anomaly detector. This flexibility gives the proposed soft
     Time         311,029      19.58    41.5    0.002     99.3               computing components wide range of detection abilities and
  All Features    311,029      19.58     20.0   0.012     93.8               thorough understanding of the training data. According to [1],
                  Overall               26.16   0.004     98.10              anomaly detectors perform better than misuse detectors over
                                                                             KDD’99 dataset using various machine learning algorithms.
                                                                             One explanation to this might be due to the complex
TABLE VIII.      EXPERIMENTAL RESULTS FROM FCM USING CORRECTED TEST          distribution of the training samples and the embedded attack
                                DATA                                         patterns in the KDD’99 data [34].
                                           # Detection Records                   Due to this reason, we have randomly selected data
                             Normal
    Feature          #                   FP     FN                           partitions based on four attacks categories and normal data in
                              Rate                      Detection
      Set         Records               rate    rate                         order to test the proposed components specific to particular
                              (%)                       Rate (%)
                                        (%)     (%)                          attacks categories. These selected data partitions are taken from
  Connection      311,029      19.58     9.1    000        100               the so-called 10% KDD dataset as it represent most of the
    Content       311,029      19.58     000    000        100               attacks categories and emulates the whole KDD data. In
     Time         311,029      19.58     1.0    000        100               addition, the 10% KDD had a very large number of records and
  All Features    311,029      19.58    11.34   000       95.36
                  Overall               5.36    000       98.84
                                                                             hence requires long training time. The data partitions are
                                                                             randomly selected and their distribution samples are illustrated
                                                                             on the following tables.
TABLE IX.        EXPERIMENTAL RESULTS FROM SOM-FCM USING CORRECTED
                              TEST DATA                                       TABLE XI.        SAMPLE DISTRIBUTION OF THE FIRST SELECTED DATA SET

                                           # Detection Records                                       Normal       Probe      DoS      U2R       R2L
                             Normal
    Feature          #                   FP     FN                            SOM-FCM Normal         1000        300        600      050      500
                              Rate                      Detection
      Set         Records               rate    rate                          SOM-FCM Probe          1000        300        600      050      500
                              (%)                       Rate (%)
                                        (%)     (%)                           SOM-FCM DoS            1000        300        600      050      500
  Connection      311,029      19.58    15.51   9..82    96.63                SOM-FCM U2R            1000        300        600      050      500
    Content       311,029      19.58     000    4.68     60.14                SOM-FCM R2L            1000        300        600      050      500
     Time         311,029      19.58     000    4.58     60.45
  All Features    311,029      19.58    9.520   6.44    90.86709
                                                                             TABLE XII.       SAMPLE DISTRIBUTION OF THE SECOND SELECTED DATA SET
                  Overall               6.25    3.92     77.02
                                                                                                     Normal       Probe      DoS      U2R       R2L
                                                                              SOM-FCM Normal         15000       3000       6000     100      5000
                                                                              SOM-FCM Probe          15000       3000       6000     100      5000




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                                                                                                            ISSN 1947-5500
                                                                                   (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                                             Vol. 8, No. 2, 2010
 SOM-FCM        DoS         15000        3000             6000   100     5000                FCM. As expected, there are exists a very complex relation
 SOM-FCM        U2R         15000        3000             6000   100     5000                among the data features. This condition goes worse when we
 SOM-FCM        R2L         15000        3000             6000   100     5000                detecting patterns from large dataset. Therefore, the test data
                                                                                             must be always reduced for processing in intrusion detection.
   In Figure 8, we have demonstrated the classification and                                  We believe that by reducing to the minimum number of feature
detection rates of the overall tests data cases which synopsis                               we can significantly improve the classification, training time
the overall tests results in the majority of cases. In fact, to                              and hence improve the detection process. Figure 10 shows the
obtain the desired detailed results about some cases we need to                              overall assessment based on the specific features selection
run tests over 10 times for particular case to show all possible                             method used.
graphics.
                                                                                               120

                                                                                               100
  120
                                                                                                80
  100                                                                                                                                                     FP Rate
   80                                                                                           60                                                        FN Rate
                                                                            Set1
                                                                                                                                                          Detection Rate
   60                                                                       Set2                40

   40
                                                                                                20
   20
                                                                                                 0
     0                                                                                               Connection    Content     Time        All
                                                 e



                                                         e
                 e
       al




                              2R




                                          io L
                                               at
                        S




                                                                                                                                         Features
                                                       at
                b
     rm




                                              2

                                              R
                       o
              ro




                                             R




                                                      R
                      D



                             U




                                            n
    o



             P




                                                      P
   N




                                                     F
                                        ct
                                      te




                                                                                               Figure 10. Detection records using various features in majority of cases.
                                     e
                                    D




            Figure 8. SOM-FCM classification and detection rates.                                We have conducted a test for the online generated data. The
                                                                                             objective of this test is to show the effectiveness and the
   From the obtained results, we can notice that SOM-FCM                                     suitability of the approach for real-time intrusion detection.
method can give high detection and classification rates in                                   Typically, the sniffer components collect network traffic data
majority of cases. It is also clear that the higher the number of                            in a promiscuous mode which make the whole network data
data samples the lower detection of normal data patterns. One                                has same factors of being suspicious or normal. This condition
                                                                                             usually triggers full detection rate of all cases. However,
explanation to this result could be the noise and the irregular
                                                                                             normal traffic data present a few false positives due to some
patterns of attack and normal classes embedded in the dataset                                factors that are not representing the simultaneous connections
[35]. The evaluation presented in Figure 9 shows the detection                               such that features occurrences and relevancies from live
records versus the false positive records in majority of cases.                              network generated data are not balanced over a certain period
The figure shows the significantly decrease of false positives                               of time. In this study, the content of the packet headers are used
and the detection improvements using SOM-FCM.                                                such as (TCP, UDP, and ICMP) and the features are portioned
                                                                                             regard to the packet headers accordingly. For the real-time
  120
                                                                                             intrusion detection test, the collected network data are initially
                                                                                             treated as normal while we running our antivirus software in
  100
                                                                                             parallel during the test which later realized as anomalous.
   80
                                                                  FP Rate                        Figure 11 shows the overall online detection records. The
   60
                                                                  Detection Rate             figure shows that the detection rates were almost the same for
   40
                                                                                             most of the detection cases and the normal treated online
   20                                                                                        generated data was detected as anomalous. One explanation to
    0                                                                                        this situation might be the irregular relevance of the data
         Single SOM   Multiple
                       SOM
                                    FCM         SOM-FCM
                                                                                             patterns and the noise of the network traffic flow.

                                                                                               120
         Figure 9. SOM-FCM Detection rates vs. false positives rates.
                                                                                               100
    The performance measure of SOM, FCM and the
                                                                                                80                                                         Single SOM
combination SOM-FCM with specific features populations was                                                                                                 Multiple SOM
tested because of reasons mentioned in [36]. We considered the                                  60
                                                                                                                                                           FCM
feature selection based on content, time and connection                                         40                                                         SOM-FCM

according to Minnesota IDS, MINDS [37]. It was clear that                                       20
there is a prime importance of the connection features in
various attack detection such that they can help in reduce false                                 0
                                                                                                      Anomalies    FP Rate     FN Rate    Detection
positives in most of the cases. We also notice that the SOM                                          percentage                            Rate
method triggers more false positives and false negatives
without the basic features as compared with FCM and SOM-                                                          Figure 11. Online detection records.




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                                                                                                                             ISSN 1947-5500
                                                             (IJCSIS) International Journal of Computer Science and Information Security,
                                                                                                                       Vol. 8, No. 2, 2010
    The experimental results show that causal reasoning is a                  Based on the domain knowledge of network data, the
vital approach for intrusion detection. It was also clear that            proposed FCM framework uses a causal reason to measure the
studying the probability of action of odd and attack neurons is           severity on network data. False positive alerts have been
of prime importance in order to trace attacks details and reduce          addressed by various studies for real-time operations [11, 12,
number of false positives. We believe that further improvement            and 15]. These studies whether are concentrating on speed
on SOM-FCM structure will improve the detection accuracy                  detection or certain method improvement. On the other hand,
and expose more information about attacks details. For future             false positive alerts have been addressed by various studies at
research, experiment should be done on comprehensive real-                sensor level [16, 17, and 18] by improving the sensor outputs.
time environment and investigating methods for intelligent                These studies whether are too general or concentrate on certain
features selection and presentation.                                      product improvement. Moreover, false alerts have been tackled
                                                                          at higher levels of the IDS operations. One such prototype is
                                                                          the Toolkit for Intrusion Alert Analysis [19], and the Intrusion
                      VI. RELATED WORK                                    Alert quality Framework [20] that uses certain quality
    Most of the intrusion detection research focuses on the               parameters to improve the false positives using DARPA 2000
detection and classification methods. Unfortunately, existing             data set.
systems failed in completely assessing the false alerts
                                                                              The various techniques used include data mining [21], AI
generation problem as well as the features and data attributes
                                                                          techniques [13], fuzzy logic [22], neural networks [23] and
selection dominantly.
                                                                          neuro-fuzzy approach [24]. These techniques and approaches
    Recently, the interest on artificial intelligence (AI)                work on logs/alerts directly and indirectly by building new
techniques and data mining applications have received greater             strategies to tackle intrusions of various types to improve the
attention; particularly the use of unsupervised leaning methods           detection process. Other reported research work tackled the
as they have the ability to address some of the short comings             detection accuracy from the features selection perspective by
for IDS [11]. This is also helps to achieve the ultimate goal for         ranking features subsets to represent different type of attacks
the IDS i.e. the capability of novelty detection. The                     [25, 26]. Here, we have considered features selection to be self
unsupervised learning method so-called self organizing maps               extracted and learned.
(SOM) has represented an excellent performance for sensors
                                                                              In this study, we have established a link between SOM,
work on unsupervised learning mode [2] as well as it is
                                                                          FCM and used the combination for building better IDS sensor.
efficient for real-time intrusion detection [12]. However, in
                                                                          Also the initial application of FCM and SOM architecture to
order to refine the process and achieve better detection and
                                                                          the IDS problem has been reported [13, 2]. The focus of this
performance, extra efforts are required. On the other hand,
                                                                          research work will be on how practitioners can answer to
current trends on IDS didn’t simply go for novelty detection
                                                                          specific elements or issues regarding the internal properties of
but also to improve the reliability issues in term of detection,
                                                                          events of SOM and FCM that have a specific influence on the
false positives, adaptability, speed and real-time issues.
                                                                          performance of SOM-based intrusion detectors. The issues
    To our best knowledge, existing studies on causal                     addressed in this study highlight question on how to eliminate
knowledge acquisition for intrusion detection are very limited.           ambiguities of odd neurons by extracting and presenting the
However, our work was also motivated by the work done                     most related features and factors.
recently on the intelligent IDS prototype [13] and the probe
                                                                               The immediate result of this research is to improve the
detection system (PDSuF) prototype [14]. The proposed
                                                                          detection deficiency issue in the SOM-based IDS sensors by
intelligent IDS system [13] use fuzzy rule based and FCM as
                                                                          reducing the false alerts and increasing the detection accuracy
decision support tools and inference techniques. The proposed
                                                                          at the sensor level. We believe that the biggest challenge here is
decision engine analyzes both misuse and anomaly modules
                                                                          to develop an intelligent inference engine to defense-in depth
information and combine both results for generating the final
                                                                          i.e. able to deal with uncertainty and detect novel attacks with
reports. For misuse information, the decision engine assesses
                                                                          low rate of false alerts. Moreover, any optimal solution of an
the results from different misuse modules in order to capture
                                                                          adaptive IDS system should provide the means of real-time
misuse scenario. The anomaly detection module information is
                                                                          detection and response as well as high level trust among the
represented by neural networks as neurons, weights and
                                                                          IDS components.
relationship between the nodes.
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