And now Microsoft is accusing Yahoo of collaborating with Google to force Microsoft out of the search advertising business.

The latest twist in the long-playing Yahoo/Microsoft saga has surfaced in a Senate judiciary subcommittee hearing that will help determine if the Google/Yahoo advertising deal signed in April should go ahed.
Microsoft counsel Brad Smith testified that Yahoo's CEO Jerry Yang had told Microsoft that the search advertising market was polarised with Google on one side; yahoo and Microsoft on the other.
Apparently, he said that a deal between Google and Yahoo would leave Microsoft exposed and unable to stand on its own.
Smith also told the subcommittee that the Google/Yahoo deal would make Google the major player in the market, with 90% of the market.