Microsoft is getting another chance to prove to the US Patent and Trademark Office (USPTO) that the disputed Eolas patent for browser plug-ins is invalid.

The two companies have fought for eight years over the ownership of running executables in a web browser. US courts have awarded Eolas over $500m in the fight, but the ruling was overturned at appeal.

The USPTO upheld the ownership and validity of Eolas's patent in 2005, but has agreed to re-examine the issue. Last Friday, Microsoft announced a five-judge panel at the USPTO will hear evidence from both sides. Microsoft now claims to own an earlier, but more general, patent that covers the same ground as Eolas's patent.

Eolas's IP is owned by the University of California and licensed to the tiny firm. Both the University and Eolas sued Microsoft in 1999, alleging the implementation of ActiveX in Internet Explorer infringes on their intellectual property.

In 2003, a jury agreed with the claim, awarding damages of $520.6m and interest. In response, Microsoft released a patch containing new code that works around the Eolas patent.

Microsoft successfully appealed the case on March 2005, winning a retrial on the claim that a lower court incorrectly blocked evidence of prior art. This is scheduled in Chicago federal court on July 9.

According to Microsoft, a web browser named Viola, created by software engineer Perry Wei a year before the UC patent filing date, uses a similar plug-in implementation. Wei had written the program when he was a student at the University of California at Berkeley. ®

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