Microsoft has unilaterally changed the conditions for the Novell SuSE certificates that it sells to customers. 

The move is intended to prevent Microsoft being subjected to the GPLv3 open source licence published on 29 June. 

If Microsoft is bound by the GPLv3, it would be forced to provide a royalty-free patent licence to all users, developers and distributors of GPLv3 software.

The phenomenon is referred to as GPLv3 contamination, which Microsoft is trying desperately to prevent. 

"Microsoft has decided that the Novell support certificates that we distribute to customers will not entitle the recipient to receive support from Novell, or any other party, nor any subscription for support and updates relating to any code licensed under GPLv3," the company said in a statement on 5 July.

To customers, the move means that the certificate will not offer them support for GPLv3 software.

The move surprised Mark Radcliffe, a partner and software licensing expert at Silicon Valley law firm DLA Piper. 

"What is interesting is that Microsoft is reacting to the GPLv3 so quickly," he told vnunet.com. 

"They never expressed their concerns. They never said: 'Look, we're going to pull the trigger and pull any GPLv3 code if you put this provision in.' I guess they decided that they didn't like the risk level that they going to take."

Although the Linux kernel itself is unlikely to switch to GPLv3, several components bundled with the kernel to form what is described as Linux have alre ady adopted the new licence.

Over time it is expected that Linux distributions will combine GPLv2 and GPLv3 components.

The certificates in question are part of the partnership that Microsoft and Novell signed in November.

As part of the agreement, Microsoft paid $240m for 70,000 coupons that entitle the owner to a free multi-year subscription to Novell's SuSE Linux Enterprise Server software. 

Technically the certificates entitle the holder to support from Novell. Microsoft merely provides the coupons to the user.