Microsoft has filed a patent infringement lawsuit against navigation device maker TomTom. The suit alleges that several of TomTom's products, including some that are Linux-based, infringe on a handful of Microsoft's patents. Several of the patents in question relate to car computing systems and navigation, but there are also two that cover Microsoft's FAT32 filesystem. If Microsoft begins to systematically enforce its FAT32 patents, it could have broad ramifications for the Linux platform and for mobile device makers.

The lawsuit, which was reported today at Todd Bishop's Microsoft blog, is thought to be the first time that Microsoft has directly targeted Linux with patent litigation. In an interview with Bishop, Microsoft deputy general counsel for intellectual property Horacio Gutierrez claims that this is not the beginning of a broader intellectual property campaign against Linux. Gutierrez characterizes the lawsuit as a last resort option that Microsoft is pursuing after attempting to negotiate a private settlement with TomTom for over a year.

Two of the patents in question are #5,579,517 and #5,758,352 which cover techniques for implementing a "common name space for long and short filenames." The patents basically cover a backwards compatibility hack that Microsoft implemented in its filesystem to preserve compatibility with the filename munging scheme that was used in MS-DOS where filenames were limited to 11 characters in length. The software methods described in the patent are used in modern variants of Microsoft's FAT filesystem.

Microsoft's FAT patents have been vigorously challenged in court, but were finally upheld in 2006. Eben Moglen—a Columbia University law professor and the chairman of the Software Freedom Law Center—once described the FAT patents as a "proverbial Sword of Damocles hanging over the open source community" and warned that Microsoft could use them to do immense damage to the Linux platform. Indeed, Microsoft's filesystem format is used broadly on external storage devices such as camera memory cards.

TomTom publishes a list of GPL-licensed software that is used in the company's products. One of the items on that list is dosfstools, a package of tools that are used to perform various checking and repair operations on FAT filesystems. It's not clear yet if dosfstools itself is the source of the patent infringement, but it seems likely that FAT support in general is problematic. The dosfstools package is also used on Amazon's Kindle, Google's Android platform, and Nokia's Maemo platform.

If Microsoft attempts to broadly enforce this patent against Linux users and vendors, the Open Invention Network (OIN) might decide to invoke the so-called "nuclear option" and retaliate with its own massive arsenal of software patents. The OIN, which was founded to assemble a defensive patent portfolio for protecting Linux and some open source technologies, includes patents on basic principles of computing including networking, e-business, and bytecode compilation.

Microsoft has previously made broad threats against the Linux kernel and the broader open source application ecosystem, alleging that the Linux desktop stack infringes on over 200 of the company's patents. These claims have never been substantiated and Microsoft has never disclosed specific details about which patents it believes have been infringed.

Other Microsoft patents that TomTom allegedly infringes inlcude #6,704,032, which covers "Methods and Arrangements for Interacting with Controllable Objects within a Graphical User Interface Environment Using Various Input Mechanisms", and #6,175,789 which covers methods for creating a "Vehicle Computer System with Open Platform Architecture." Microsoft is asking the court for an injunction against TomTom and treble damages for willful infringement.

Listing image by OpenTom Wiki