Linux vendors Red Hat and Novell are being sued for patent infringement by a pair of patent houses in what is believed to be the first such lawsuit involving Linux.

The plaintiffs, IP Innovation and Technology Licensing, say they own US patent 5,072,412 for a "User Interface with Multiple Workspaces for Sharing Display System Objects" issued in 1991, as well as two other similar patents.

Red Hat and Novell are accused of infringing on the patents by selling Red Hat Linux, Novell SuSE Linux Enterprise Desktop and Novell SUSE Linux Enterprise Server, according to the lawsuit filed in Texas last week.

The plaintiffs also claim that the defendants are deliberately and wilfully infringing on the patents because they were previously notified of the infringement.

IP Innovation and Technology Licensing are seeking an injunction from the court, damages, and "other relief that the court or a jury may deem just and proper," according to the lawsuit. IP Innovation is a subsidiary of The Acacia Technologies Group, a division of Acacia Research that develops, acquires, licenses and enforces technology patents.

Technology Licensing is a company that acquires and licenses intellectual property primarily in involving electronics for the television industry, according to its website.

Attorneys for IP Innovation and Technology Licensing could not be reached for comment.

"We're assessing this filing now," said Novell spokesman Bruce Lowry in an email. "Obviously, we'll defend our interests. But it's too early at this stage to talk about specifics on this case."

Red Hat could not be reached for comment.