Microsoft has finally decided to file a lawsuit against TomTom over its implementation of the Linux kernel, stirring fears that the company has begun a patent war. Microsoft has filed eight suits against TomTom in total, five of which relate to car-navigation systems, while another three deal with TomTom’s Linux use. The Redmond company has long argued that aspects of Linux violate its patents, and caused a stir back in 2007 by claiming it had counted 235 separate infringements.

The suit is a new thing for Microsoft, as the giant software company took no action against companies using Linux. Microsoft claims the suit is specific to the individual circumstances surrounding TomTom and not a shot across the bows of the wider community, even if some Linux vendors braced for a larger fight. Microsoft and TomTom failed to reach a patent-licensing agreement after more than a year of talks.

Jim Zemlin, executive director of the Linux Foundation, says the community can’t read too much into the lawsuit, as this is a private dispute between two entities concerning GPS mapping software. As for its part, TomTom representatives only said they will vigorously defend the company against the suit. Furthermore, Zemlin also said the Linux Foundation is ready to mount a defense of Linux should the need appear.

Basically, TomTom’s Linux is using an implementation of FAT to add file system support for long and short file names, memory management for flash and for connecting devices. Microsoft says TomTom misused Microsoft’s patented version of FAT32 and VFAT, but TomTom says it used a different implementation of FAT instead. It remains to be seen if Microsoft is right regarding this suit.