Ubuntu backer Canonical has declined to discuss an intellectual property deal with Microsoft as long as the company refuses to disclose the patents that it believes are violated in open source software. 

Canonical is the corporate sponsor of the Ubuntu Linux distribution. The software is best known for its desktop version of the open source operating system but also offers a server version and is developing software to run mobile devices.

The company responded to rumours claiming that Canonical would follow in the footsteps of Novell, Xandros and Linspire in signing a Linux patent licensing agreement with Microsoft. 

"We have declined to discuss any agreement with Microsoft under the threat of unspecified patent infringements," Mark Shuttleworth, founder of Canonical, wrote on his blog. 

"Allegations of 'infringement of unspecified patents' carry no weight whatsoever. We do not 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.

"A promise by Microsoft not to sue for infringement of unspecified patents has no value at all and is not worth paying for."

Shuttleworth pointed out that patent licensing companies pose a far greater risk than Microsoft, and that a Microsoft agreement would not protect users from those threats.

Patent licensing companies use patents solely to generate licence revenues and do not sell products based on the patents.

NTP last year extracted $612.5m out of BlackBerry maker RIM, and Microsoft has been in a prolonged $521m battle with Eolas over a patent that allegedly covers its Internet Explorer browser. 

Microsoft is trying to improve the interoperability between its software and open source alternatives, but continues to insist that it should be compensated for its patents that open source software allegedly violates.

The firm claimed in May that it had identified 235 patents violated by open source applications, but declined to identify any of the individual patents.

Microsoft has also repeatedly said that it has no interest in filing legal claims against individual developers or end users of open source software.

Instead of requiring users and developers to pay for its intellectual property, Microsoft is looking at Linux vendors to do so.

Ubuntu joins Red Hat in refusing to pay Microsoft for its patent portfolio.