Microsoft's prosecution of TomTom over alleged violation of patents is looking increasingly like a failure in its long-running policy of tying down Linux users through cross licensing of its IP.

Computerworld has dredged up an email exchange with Microsoft's IP and licensing legal chief that explains Microsoft's got a long history of licensing its File Allocation Table/Long File Name (FAT LFN) with companies in the car navigation space and that have specifically been using Linux and open source.

Microsoft's corporate vice president and deputy general counsel of intellectual property and licensing Horacio Gutierrez said 18 companies had signed up, including Kenwood, Alpine, and Pioneer.

According to Computerworld:

"When asked specifically if "there are companies using Linux and open-source software, which have signed FAT patent cross-licensing agreements, such as the ones, which TomTom has refused to agree to?" Gutierrez replied, "Yes, other companies have signed FAT patent licenses, both in the context of patent cross licensing agreements and other licensing arrangements."

Microsoft in earlier statements has insisted the case is not about Linux and Gutierrez denied this was the first step in a series of suits over a claimed 235 cases of Microsoft patents being violated by free and open-source software. It's worth noting that Gutierrez was one of the Microsoft legal eagles who claimed in 2007 that free and open-source software infringes those 200-plus patents. TomTom US has refused to comment on the case.

Contrary to what Microsoft may state about this not being about Linux, tying up companies that use Linux and open source in patent licensing agreements cuts to the very core of one of the things that's kept Linux and open-source alive: free distribution of the kernel and code.

Samba maintainer Jeremy Allison pointed out in a recent blog posting by writer Glyn Moody that companies who sign up to Microsoft's licensing cannot continue to distribute their code under GPLv2.

Section seven of GPLv2 - called the "Liberty or Death" clause - states that you cannot distribute code if outside restrictions have been imposed.

"What people are missing about this is the either/or choice that Microsoft is giving TomTom," Alison posted.

"It isn't a case of cross-license and everything is ok. If TomTom or any other company cross licenses patents then by section 7 of GPLv2 (for the Linux kernel). they lose the rights to redistribute the kernel *at all*."

In other words, Microsoft is eroding Linux and open source and slowing their development. A deal with Microsoft prevents GPL'd code from returning to the ecosystem whence it came, with any improvements or updates, as companies that do patent licensing deals with Microsoft must keep it in-house.

This is particularly damaging for Linux, given consumer electronics companies such as those Microsoft is tying up are making heavy use of Linux in devices from in-car systems to TVs and DVD players and could potentially return their improvements to the kernel to the market.

One reason these companies have turned to Linux and open source rather than use Windows is because of the simple expense of licensing Windows, and the fact the code is not open so they cannot make changes needed to run gadgets and devices.

"Make no mistake, this is intended to force TomTom to violate the GPL, or change to Microsoft embedded software," Allison wrote. ®