Billionaire investor Carl Icahn today responded to criticisms from Yahoo with a second open letter to the search engine giant. Addressing claims that he has no plans for Yahoo should Microsoft decline to make bid with a newly replaced board in office, Icahn says he would be willing to have Yahoo strike a search deal with Google as long as its terms would still allow a future Microsoft takeover. Icahn doesn't say whether this would still involve the proposed ad bidding system trialed earlier this year or a new plan altogether.

The investor nonetheless refuses to plan for less than a Microsoft takeover at $34.375 per share and intends to take several steps to ensure this happens, including dropping Yahoo's controversially expensive severance plan -- described by Icahn as a "poison pill" to discourage Microsoft -- as well as removing Jerry Yang from the CEO position and forbidding any partial transaction unless it nets at least the $33 per share Microsoft was offering for a takeover until it backed away from the deal. A high value for only a partial deal is unlikely and makes Icahn "skeptical," according to his letter.

The financial expert doesn't address other alternatives beyond the Google ad deal in his letter and also doesn't explain why he sees the Microsoft deal as necessary to Yahoo's future. The latter has resisted in part with claims that it foresees its recent profits continuing to grow in the next few years and thus giving it little need to sign a deal with Microsoft.

Microsoft had initially launched its bid in late January in an attempt to develop a viable rival to Google in search and search ads, but ultimately backed off after believing that Yahoo refused to accept a reasonable share price for a takeover. Yahoo in turn has maintained that it has been willing to negotiate but that Microsoft's official bids didn't assign proper value to Yahoo's assets.