In the wake of the unsuccessful Yahoo/Microsoft merger, Yahoo shareholders are venting their anger against an executive leadership they feel has failed them. Foremost among them is corporate raider Carl Icahn. Yahoo rebuffed Icahn's claims that poor management had hurt the firm, but as other institutional investors lined up behind Icahn, it became clear that the Yahoo board and its CEO were looking at a major battle for the control of the firm. The company's difficulties on both an executive and enterprisewide level underscore a host of high-level business risks facing today's public companies. For many companies, the mere arrival of Carl Icahn is enough to sound an alarm. For weak firms, it can mean that the end is nigh. For strong firms, it signals the start of a bruising war in the boardroom.