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Word that Yahoo plans to test Google search ads has Microsoft General Counsel Brad Smith and Microsoft PR all fired up. "Any definitive agreement between Yahoo! and Google would consolidate over 90 percent of the search advertising market in Google's hands," Smith said in a statement.

This would make the market far less competitive, in sharp contrast to our own proposal to acquire Yahoo! We will assess closely all of our options. Our proposal remains the only alternative put forward that offers Yahoo! shareholders full and fair value for their shares, gives every shareholder a vote on the future of the company, and enhances choice for content creators, advertisers, and consumers.

Smith once told regulators that to allow Google to merge with DoubleClick was to give it control over 80 percent of the market. That rhetoric didn't stop a merger. But maybe an extra 10 percent will do the trick this time.