The Free Software Foundation (FSF) has formed a campaign group to fight any legal action following Microsoft's claims that the Linux kernel contains code that infringes its patents.

The FSF group will have two campaign managers and an international group of volunteers, with one position to be filled by current staff member John Sullivan and the other by new appointee Joshua Gay.

"In the early years of the free software movement, the FSF worked to solve the problem of proprietary software by funding free software development," said Sullivan.

"With the creation of this campaign team, we are expanding our work to help clear the way politically and publicly for free software."

Microsoft's claim has caused uproar in the open source community and prompted withering criticism from its luminaries.

Linux kernel creator Linus Torvalds has issued a public challenge to Microsoft to detail its patent case and to stop trying to spread unease about free software.

FSF executive director Peter Brown said: "Microsoft continues to threaten the freedom of all computer users with vague claims of software-patent infringement.

"Although more people than ever before in the US have the technical capabilities to develop software, the blight of patents prevents them from making useful advancements.

"We need to determine the best way to eliminate the spectre of software patents so that free software development can flourish, and to get organised to make it happen."