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What: Shares of Vringo (UNKNOWN:VRNG.DL) fell more than 10% Tuesday, after Google asked a U.S. appeals court to overturn a previous patent judgment.

So what: Specifically, Google is asking the court to throw out a $30.5 million patent-infringement verdict won by Vringo in 2012. The trial centered around ad placement filtering technology covered under Vringo's patents and used in Google AdWords, AdSense, and Search.

Google attorneys are claiming a "fundamental failure of evidence," while one member of the court's three-judge panel stated he had "problems with the jury's findings" regarding whether Vringo had adequately proven evidence of copying.

Now what: Vringo shareholders should keep in mind this appeal only involves the 2012 verdict, not subsequent rulings in Vringo's case against Google. However, Vringo may still have the upper hand, but note Google also has pending appeals for other positive Vringo rulings. In the end, today's events serve as a reminder of just how difficult it can be for intellectual property firms to cash in against well-funded, unwilling licensees.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Google (A and C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.