All the rumors and speculation around Yahoo's future have revolved recently about Microsoft potentially buying them out. It was further rumored that Google may step in as well, or at least strike some form of deal with the ailing search company. While to many of us that seems plausible, to Microsoft that is the farthest thing from reality.
As Microsoft sees it, Google legally can't buy Yahoo because their 75% market share in online paid search makes them a near monopoly and antitrust laws would have to prevent it. A Microsoft representative even went so far as to say that their "super dominant" position makes Google the one company in the world that cannot make an offer on Yahoo.
Interestingly, this is the same company that denied they were a monopoly when Internet Explorer still enjoyed a healthy 90+ percent market share, and Windows held an even larger share of the pie. But that put aside, the Redmond-based company might have a good point as Google is the 900 pound gorilla of search today and the FTC might frown upon them trying to swallow up Yahoo.