At Microsoft's annual shareholder meeting this week, CEO Steve Ballmer emphatically closed the door on the possibility that his company was still interested in purchasing ailing Internet giant Yahoo!. His frank assessment of the situation sent Yahoo!'s stock tumbling over 20 percent to less than $10 a share.

"Let me be clear," Ballmer said at the meeting. "We are done with all acquisition discussions with Yahoo." You could almost hear the sound of Yahoo!'s stock price shatter as he finished the sentence.

Ballmer did leave one possibility open, however. He said that Microsoft was still "very open" to some sort of Internet search "collaboration." This could take the form of Microsoft purchasing Yahoo!'s Internet search business outright or the software giant entering into an agreement to work together with Yahoo! on Internet search. It's worth noting, however, that Microsoft made both offers to Yahoo! earlier this year and that Yahoo! rejected Microsoft both times. Also, Microsoft and Yahoo! are not formally discussing any kind of arrangement at this time.

Yahoo!, of course, has spent the year in a terrifying death spiral after having also rejected a mammoth $44.6 billion buyout offer from Microsoft in January. This week, co-founder Jerry Yang announced that he had agreed to step down as CEO after his promises of an internal bailout failed to materialize into a plan of any kind.