In court papers filed this week in U.S. District Court in Texas, Acacia Research, through a subsidiary called IP Innovation, filed a suit that claims the Red Hat and Novell distributions of the Linux operating system violate its patents.

The suit claims that both the desktop and server versions of Linux distributed by the two vendors infringe on three patents held by IP Innovation that describe a "user interface with multiple workspaces for sharing display system objects."

On Oct. 1, Acacia Research announced that it had hired Brad Brunell as a senior VP. Brunell joined the company from Microsoft, where he was previously the software maker's general manager for intellectual-property licensing.

While there's no evidence that suggests Microsoft is in any way connected to Acacia's suit against Red Hat and Novell, Microsoft CEO Steve Ballmer last week seemed to predict that patent firms would target the free and open source software community in the same way they've chased down commercial software developers.

"I expect they would like to go to the open source world as well," Ballmer said while speaking at a Microsoft event in the U.K. Microsoft claims Linux and other open source programs violate more than 200 of its patents.

Last year, Microsoft signed a deal with Novell that indemnifies Novell's customers from Microsoft patent claims related to Linux.

A Microsoft spokesman said via e-mail that "Microsoft is not a party to Acacia's lawsuit against Red Hat and Novell, nor are we involved in any way in this litigation." Acacia officials weren't immediately available for comment. Novell and Red Hat have yet to file a formal response to the lawsuit.