Microsoft Corp.'s move to sign patent-protection deals with Linux distributors hit a snag this week when the heads of two of the top five distributors of the open-source operating system publicly dismissed the possibility of such a partnership.

Microsoft has been actively pursuing deals with Linux distributors similar to the one it signed last November with Novell Inc., in which both companies agree not to sue each other for patent claims and to partner to make their operating systems more compatible.

The company stepped up the pressure last month when a top lawyer for the software giant told Forbes magazine that open-source software infringes on more than 235 of Microsoft's patents.

In the last month, Microsoft has signed two deals with distributors Xandros Inc. and Linspire Inc.

However, the heads of Mandriva and Canonical, the company behind Ubuntu, both wrote in blogs this week that they had no interest in such a deal.

"Interoperability between the Windows and Linux world is important and must be dealt with, and anything that helps this interoperability is a good thing," Mandriva chief executive Francois Bancilhon in a blog posting on the company's website on Tuesday, adding "the best way to deal with interoperability is open standards."

Bancilhon's sentiments echoed an earlier statement from Canonical head Mark Shuttleworth posted on Saturday. Shuttleworth quashed rumours that Ubuntu might be the next distributor to sign a deal, suggesting Microsoft's tactics were unlikely to work.

"Allegations of 'infringement of unspecified patents' carry no weight whatsoever," Shuttleworth wrote. "We don’t think they have any legal merit, and they are no incentive for us to work with Microsoft on any of the wonderful things we could do together."

Getting Microsoft's software to be compatible with Linux operating systems has become an industry-wide issue, not so much in the consumer world but with computer servers, where Linux is more widely used.

But sharing knowledge brings up the sticky question of who owns that knowledge, and this question of intellectual property ownership is at the heart of the tension between Microsoft and open-source software firms.

Underlying code restricted

Microsoft programs such as Windows or Office run on proprietary source software, meaning the underlying computer code is restricted and guarded by patent and other intellectual property protections.

Open-source software such as Linux, on the other hand, encourages individuals to add to or modify the software without fear of legal repercussions, so long as they abide by the conditions of the general public licence, which stipulates that the program must remain open and sharable.

Both Bancilhon and Shuttleworth said they were open to collaborating with Microsoft, as long as such collaboration kept their operating systems open and did not require the signing of any patent-infringement deals.

Ubuntu is the most popular Linux distribution in the world, according to monitoring site DistroWatch. Novell's OpenSUSE is second, followed by Red Hat's Fedora and the Debian and Mandriva operating systems.