Computer Viruses - Slide 1

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Computer Viruses - Slide 1 Powered By Docstoc
• Why are computer networks vulnerable?
• Methods used by hacker to gain unauthorised
• Viruses
  –   Different type of viruses
  –   How do viruses infect computers
  –   Methods used by anti-virus software
  –   Symptoms of virus infection
  –   Steps to take to protect your computer from viruses
  Brief History of Computer

With the explosive growth of the
Internet, there has been a rise in
importance of computer security
      Why are networked systems
• Internet is 37 years old
      • Was designed without security provisions
      • Communication protocols (TCP/IP) were designed when the
        security was not an issue.
      • Security features had to be layered at the top of the design

• Old operating systems were design for a single user
      • No security was need

• Explosive growth of desktops started in ‘80s
      • Also no emphasis on security

• Explosive growth started in mid-‘90s
      • Security not a priority until much later
Computer security was ignored
• Interest in computer security very old
     • But largely confined to the military
• Other communities did not care
     • Internet - it‘s only a research network, who would
       attack it?
     • Desktops - who needs military security, I just want
       to run my spreadsheet!
             Important event
• Morris worm - 1988
    • Brought down a large fraction of the Internet
    • Academic interest in network security

• E-commerce - mid ‗90s
    • Industrial interest in network security protocols

• Resurgence of worms - early ‗00s
    • Made computer security a household term
   Modern operating systems
• Improved security in modern operating
  – Challenge for hackers
  – Hackers did not give up
  – more sophisticated virus were born.
  – Security is still a major issue in networked
    Unauthorised logins and password
•   Intruders use various ways to access someone‘s account
     – Brute force:
         • Program making successive login attempts
     – Domain knowledge:
         • Users tend to use passwords easy to remember
              – Partner‘s name, …
     – Mock login:
         • If a hacker has physical access, they might install a program simulate the screen image
           of the login prompt and store userid/password.
     – Human factors:
         • Call the computer help desk claiming you forgot your password.
         • Reformed hackers, the best way to get information is to ask for it.

     – Spyware:
         • malicious code that gains access to a computer via a Trojan Horse
         • can monitor the user‘s keystrokes and report passwords, credit card numbers
         • etc to the hacker via a TCP/IP connection
                                    Virus Growth

                             1988     1990     1993   1999

•   1988:   Less than 10 known viruses
•   1990:   New virus found every day
•   1993:   10-30 new viruses per week
•   1999:   45,000 viruses and variants
A Couple of Definitions:
• A computer virus is a computer program
  that can copy itself and infect a computer
  without permission or knowledge of the
• ―a program that replicates by ―infecting‖
  other programs, so that they contain a
  copy of the virus‖
• Viral code is attached or ―inserted‖ into the order
  of execution so that when the legitimate code is
  run the viral code is also run or run instead of
  the legitimate code.
• May be ―tacked‖ on to the end of an executable
  file or inserted into unused program space.
• Cavity viruses:
   – Overwrite part of a legitimate program
   – Hard to detect as file size is not modified
• Overwrite boot records:
   – Viruses starts executing when the computer starts up
The Normal Virus works like this:
• User call for a legitimate program

• The virus code, having inserted itself in the
  order of execution, executes instead or in
  addition to the legitimate program.

• The virus code terminates and returns
  control to the legitimate program
How they work:
         Basic structure:
             look for one or more infectable objects
             if (none found)
               infect object
Doesn‘t remain in memory, but executes all of the viral code at once
then returns control to the infected program
A computer WORM:
  • is a self-contained program (or set of programs),
  that is able to spread functional copies of itself or its
  segments to other computer systems via network
  • worms do not need to attach themselves to a host
  • 2 types of worms
     •host computer worms
     •network worms.
 NETWORK- Computer Worms

• Network worms consist of multiple parts, called
   •The segments run on different machines on the network
   •and may even perform different actions

      • Moving   a segment from one machine to another is only one of
      their purposes.
    HOST- Computer Worms
Host computer worms:
  • are entirely contained in the computer
  they run on.
  • use network connections only to copy
  themselves to other computers.
  •the original terminates after it launches a
  copy on to another host.
     • Only one copy of the worm running
     somewhere on the network at a time
      How Viruses are born
• Unlike biological viruses, computer viruses
 do not simply evolve by themselves
  – deliberately created by programmers, or by
    people who use virus creation software
         How Viruses are born
 • Viruses are written as
    – research projects

    – to attack the products of specific companies,

    – to distribute political messages,

    – and financial gain from identity theft,

 • Some virus writers
    – consider their creations to be works of art

    – See virus writing as a creative hobby

Releasing computer viruses is a crime in most jurisdictions
  Viruses can avoid detection
• To avoid detection by users, viruses employ different deception

   – They do not make themselves to
       • change the date of last modified

       • increase file sizes

       • damage the files

   – They kill the tasks associated with antivirus software before it
      can detect them
             Logic Bomb:
• Logic Bomb: A logic bomb executes when
  specific conditions occur.
• Triggers for logic bombs can include
  change in a file, by a particular series of
  keystrokes, or at a specific time or date.
• Trapdoors allow access to a system by
  skipping the usual login routine.
• Overall goal of rootkits: install trapdoors
              Macro Viruses
• Macro virus:
  – Encoded as macro and embedded in a document.
  – Many applications allows you to embed a macro in a
  – Microsoft Word, Excel, Access
  – The macro executes each time the document is open.
  – Infect programming environments rather than files
  – Once a macro virus gets onto your machine, it
    embedded itself in all future documents you create
    with the application
  – 75% of all viruses today are macro viruses
  Why are they so dangerous?
• Can infect multiple types of operating
• People don‘t normally think of viruses in
• Easy to learn how to write a macro virus
• Because office programs are usually
  integrated, email programs can be used to
  further spread the virus
      Famous Macro Viruses
• Concept: - Distributed by Microsoft
  – Considered to be the first macro virus
  – Simply showed the potential for macro viruses
   History of some well known
• 1999 The Melissa virus:
  – is a macro virus,
  – It uses Microsoft Word to infect computers
    and is passed on to others through Microsoft
    Outlook and Outlook Express e-mail
  – Overwrites first macro in open documents and
    in the template
  – Turns off macro detection
             Viruses (Con‘t)
• 2000 The "I Love You Virus"

  – wreaks havoc around the world.

  – It is transmitted by e-mail and when opened,
    is automatically sent to everyone in the user's
    address book
– July 2001: The Code Red worm

     • infects tens of thousands of systems running Microsoft
       Windows NT and Windows 2000 server software.

     • causing an estimated $2 billion in damages.

     • The worm is programmed to use the power of all infected
       machines against the White House Web site at a
       predetermined date.

     • the White House deciphers the virus's code and blocks
       traffic as the worm begins its attack.
               Viruses (con‘t)
• 2002: Melissa virus author David L. Smith, 33, is
  sentenced to 20 months in federal prison

• Jan. 2003: The "Slammer" worm
  • infects hundreds of thousands of computers in less
    than three hours.
  • The fastest-spreading worm ever wreaks havoc on
    businesses worldwide, knocking cash machines
    offline and delaying airline flights.
                 Viruses (Con‘t)
• 26 January 2004, MyDoom:
  – The Mydoom virus is first identified around 8am.

  – Computer security companies report that Mydoom is responsible
    for approximately one in ten e-mail messages at this time.

  – Slows overall internet performance by approximately ten percent
    and average web page load times by approximately fifty percent

  – 1 February: An estimated one million computers around the
    world infected with Mydoom begin the virus's massive distributed
    denial of service attack—the largest such attack to date
               Virurses (Con‘t)
• 2007: A new virus called "Storm Worm." is released.

• This fast-spreading email spammer disguises itself as a
  news email and asks you to download film.

• The "Storm Worm" gathers infected computers into a
  botnet, which it uses to infect other machines.

• It was first identified on Jan. 17 and within 13 days had
  infected 1.7 million computers
• 2009 "Conficker" worm:
  • 9 million computers running on Windowsoperating system were

   • The malware spread via the Internet and the main tools that
     helped the worm spread were unpatched corporate networks
     and USB memory sticks.

   • t loads itself on to a computer by exploiting a weakness in
     Windows servers.

   • Once it has infected a machine, the software also tries to
     connect to up to 250 different domains with random names every
         Other type of viruses
•   Trojan horse
•   Denial of service (Dos)
•   Distributed DoS attacks
•   Remote Administration Trojans (RATs)
•   Buffer Overflow attack
     The Original Trojan Horse
• Trojan horses are
  named after Homer‘s
  Iliad story of Greeks
  gifting a huge wooden
  horse to Troy that
  housed soldiers who
  emerged in the night
  and attacked the city.
            Trojan Horses
• Trojan horses are programs that appear to
  have one function but actually perform
  another function.
• Modern-day Trojan horses resemble a
  program that the user wishes to run - a game,
  a spreadsheet, or an editor. While the
  program appears to be doing what the user
  wants, it is also doing something else
  unrelated to its advertised purpose, and
  without the user's knowledge.
Denial-of-Service (DoS) Attacks
• DoS attack
  – Prevent a system from servicing legitimate requests

  – In many DoS attacks, unauthorized traffic saturates a network‘s
    resources, restricting access for legitimate users

  – Typically, attack is performed by flooding servers with data packets

  – Usually require a network of computers to work simultaneously,
    although some skillful attacks can be achieved with a single machine

  – Can cause networked computers to crash or disconnect, disrupting
    service on a Web site or even disabling critical systems such as
    telecommunications or flight-control centers
      Distributed DoS attacks
• Programs of this type
  – Spread to as many hosts as possible
  – Wait for predefined commands or fixed date
    and time to lunch denials of Service
  Remote Administration Trojans
• Once installed on PC.
  – Give hackers complete control
    • They can record keystrokes, web access,
      copy/delete files
    • RATs consists of client and server:
       – The server somehow installed on the victim‘s computer
       – Attempt to contact the hacker‘s system (client)
           Software Exploitation
• Buffer overflow attacks
   – Occurs when an application sends more data to a buffer than it
     can hold

   – Can push the additional data into adjacent buffers, corrupting or
     overwriting existing data

   – A well-designed buffer overflow attack can replace executable
     code in an application‘s stack to alter its behavior

   – May contain malicious code that will then be able to execute with
     the same access rights as the application it attacked

   – Depending on the user and application, the attacker may gain
     access to the entire system
        Buffer Overflow Injection
• buffer overflow, or buffer overrun,

• is an anomaly where a program, while writing data to a buffer,
  overruns the buffer's boundary and overwrites adjacent memory.

• can be triggered by inputs that are designed to execute code, or
  alter the way the program operates

• Steps
   – Inject attack code into buffer
   – Redirect control flow to attack code
   – Execute attack code
        Types of Propagation
• Parasitic
  – Propagates by being a parasite on other files.
  – Attaching itself in some manner that still leaves the
    original file usable.
  – .com and .exe files of MS-DOS
  – Macro virus
• Boot sector infectors
  – Copy themselves to the bootable portion of the hard
    (or floppy) disk.
  – The virus gains control when the system is booted.
 How Antivirus software works?
• Detect using a list of virus signature definitions

   – comparing the files stored on fixed or removable

     drives (hard drives, floppy drives), against a database

     of known virus "signatures".
 How Antivirus software works?
• Heuristic detection:
  – Use a heuristic algorithm to find viruses based on

    common behaviors

  – Looks for code which is similar to known viruses

  – Or monitor suspicious activities
     • Attemting to write to system files or boot records.
 How Antivirus software works?
• File size changes:
  – Are monitored
  – Difficult to detect cavity viruses as the file size
    will not necessarily change.
 How Antivirus software works?

• Some anti-virus programs gives you a
 real time protection
  – Examin files as they are being opened,
   downloaded,       copied,   accessed,   and
   transmitted etc
 How Antivirus software works?

• They need regular updates
  – in order to gain knowledge about the
   latest threats
 Damage prevention & data recovering

    How to prevent damages caused by viruses?

• Take regular backups (including OS) on different

  media, unconnected to the system (most of the

 Keep your computer Virus free
• Install reliable anti-virus software
  – the most important step you can take towards keeping

    your computer clean of viruses

• Update your anti-virus software regularly
  – variations of viruses and new ones can be slipped if your
    software is not current
 Keep your computer Virus free
• Get immediate protection
  – Configure your anti-virus software to boot automatically on
    start-up and run at all times
 Keep your computer Virus free
• Don't automatically open attachments
  – ensure that you examine and scan email and other
    attachments before they run as they might contain viruses

  – Activate macro virus protection in your word processor

  – Check security setting in your web browser.

• Scan all incoming email attachments
  – Do not open any email attached files if the subject line is
    questionable, unexpected or the source (address) is
 Keep your computer Virus free
• Delete chain emails and junk email
  – Do not forward or reply to any of them, they clogs up the

  – Some viruses can replicate themselves and spread
    through email as a chain
    Symptoms of virus infections
• Delay in start up, loading files and programs
• Increase in program size files
• Shortage of disk space or memory
• New file names or file dates/times
• Files deleted unexpectedly
• Computer crashes
• Message or images appearing on the screen
• Ms-word macro protection warns that a file
  contains macros.
• Anti-virus software reports a virus
• Computer network are vulnerable
• Methods used by hacker to gain unauthorised
• Viruses
  –   Different type of viruses
  –   How do viruses infect computers
  –   Methods used by anti-virus software
  –   Symptoms of virus infection
  –   Steps to take to protect your computer from viruses
• Symantec Anti-virus centre
• Centre for computing and social Responsibility (CCSR)
• CERT: Centre at Carnegie-Mellon University USA
• Risks forum: online discussion about security issues
• CIAC: site hosted by US Dept of Energy
          – Dealing with hoax virus alerts
• Microsoft:
Thank you
Good luck