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Yahoo CEO Scott Thompson

Yahoo grabbed the attention of the tech industry today, but not with a new product announcement. The company filed a patent infringement lawsuit against Facebook, a bold move under the leadership of new CEO Scott Thompson.

In other words, one of Microsoft’s biggest partners just sued another of Microsoft’s biggest partners, a company in which Microsoft has a minority stake.

As noted by Matt Rosoff of Business Insider, Facebook has a mere 20 patents to its name, and the natural thing would be for the company to call up its minority shareholder, Microsoft, in search of a patent licensing agreement to use in its defense.

But Microsoft is counting on its partnership with Yahoo to give it the critical mass to compete against Google in the search market.

“Excuse, me, Mr. Myhrvold? Mark Zuckerberg on line two.”

At the very least, putting together the invite list for this year’s CEO Summit in Redmond just got a lot more challenging.

Yahoo’s suit takes aim at Facebook with 10 patents, in such areas as personalized ad targeting, music playback, content sharing and other aspects of the Facebook experience.

Kara Swisher of AllThingsD has a copy of the lawsuit, and details on the back-and-forth between the companies, including Yahoo’s quote of Facebook CEO Mark Zuckerberg: “Getting there first is not what it’s all about.”

PaidContent has a summary of the patents that Yahoo is using as the basis of the suit.

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