Yahoo and Carl Icahn dueled Thursday as the corporate raider vowed to overthrow the firm's board and the Internet pioneer fired back that the billionaire misunderstood Microsoft's failed takeover bid. Icahn said in an open letter that Yahoo "completely botched" merger talks with Microsoft and that he is amassing Yahoo stock to oust the board of directors at an annual shareholders meeting on July 3. "Unfortunately, your letter reflects a significant misunderstanding of the facts about the Microsoft proposal and the diligence with which our board evaluated and responded to that proposal," Yahoo board chairman Roy Bostock wrote in an open response to Icahn.