Open sourcers have asked German authorities to probe a Microsoft-backed purchase of hundreds of patents owned by Novell as part of that company's purchase by Attachmate.

The Open Source Initiative (OSI) has written to the German Federal Cartel Office saying that the purchase of 882 patents for $450m by never-heard-of-before CPTN Holdings "represents a potentially new, and unprecedented threat against open source software."

The patents are being unloaded as part of Novell's acquisition by Attachmate. Little is known of CPTN other than that it's led by Microsoft and its members include Apple, Oracle, and EMC.

OSI president Michael Tiemann blogged over the Christmas holiday that his group was moved to act once it learned that Microsoft had recruited the other three to join CPTN.

The Cartel Office is Germany's national competition regulator. It has fined Microsoft millions of dollars over anticompetitive pricing of Office in past years. The Office was open to comments on the Novell transaction.

According to the OSI, the formation of CPTN "represents a MAJOR disruption to the competitive landscape." It claims that the principle members see Linux and open source as "major" threats to their businesses and had made hostile statements towards open source.

In his blog posting announcing the OSI request to the German authorities, Tiemann wrote: "The fact that Microsoft was leading the takeover of Novell's patents was itself alarming to the open source community, but when it was revealed that Microsoft had recruited Oracle, Apple, and EMC to be co-owners of the patents, the OSI Board felt compelled to request that competition authorities take a closer look at the proposed transaction."

In its statement to the Cartel Office (PDF), the OSI wrote: "Whereas Novell was sincere in promoting and participating in open source software development and had an incentive to maintain their patent assets as a defensive portfolio, CPTN has all the motives and opportunity to do the opposite.

"That is, they have no incentive to support open source as a competitive alternative to proprietary software. CPTN creates a cover to launch patent attacks against open source while creating for each principal a measure of plausible deniability that the patent attack was not their idea."

Novell's sale to Attachmate and the unloading of the 882 patents was announced in November of last year. At the time, it was known only that Microsoft was leading CPTN, and such was the outcry given Novell's status as the owner of Unix that Novell was forced to issue a statement saying it would continue to own the Unix copyrights following completion of the Attachmate deal.

While that might have caused a sigh of relief, it still remains unclear what patents exactly are being sold to CPTN.