Novell and Microsoft have exchanged punches over Microsoft's claim that Linux infringes its intellectual property. 

In an open letter to the open source community published on 20 November, Novell chief executive Ron Hovsepian denied an IP-ownership claim by Microsoft. 

"Our agreement with Microsoft is in no way an acknowledgment that Linux infringes upon any Microsoft intellectual property," Hovsepian wrote.

"When we entered the patent cooperation agreement with Microsoft, Novell did not agree or admit that Linux or any other Novell offering violates Microsoft patents."

The disagreement revolves around the Microsoft Novell partnership signed earlier this month.

In addition to distribution and interoperability agreements for the companies' software products, the two also created a patent covenant in which Microsoft promises not to enforce its intellectual property against users of Novell Linux, as well as individual software developers.

Novell's open letter prompted Microsoft to send out a press release on Monday stating that the two companies "have agreed to disagree" on the intellectual property issue.

"The agreement between our two companies puts in place a workable solution for customers for these issues, without requiring an agreement between our two companies on infringement," Microsoft said.

Microsoft chief executive Steve Ballmer ignited the row last Thursday when he said that the partnership was in part inspired by "the fact that [Linux] uses our patented intellectual property [which] is a problem for our shareholders".

Some observers initially considered the partnership as a major step towards a patent truce between Microsoft and Linux.

Microsoft enforcing its intellectual property portfolio against Linux users, developers or distributors is generally considered the greatest potential threat against the operating system.

Ballmer's comments reignited those fears, and underscored the notion that the software behemoth is looking to use its patent portfolio to levy an innovation tax on open source.