In Microsoft vs. TomTom, Microsoft is suing TomTom in part because the guys from Redmond claim that TomTom's use of Linux in its navigation devices has violated three of its file-system related patents. One reason why Microsoft feels it can do this is that it already has patent cross-licensing agreements covering these patents with other Linux-using companies.
I dug this up during an e-mail discussion with Horacio Gutierrez, Microsoft's corporate vice president and deputy general counsel of intellectual property and licensing, Gutierrez said, "We have a history of licensing the patents in this case through patent cross licensing agreements with other leaders in the car navigation space, including Kenwood, Alpine and Pioneer, and through our FAT LFN (File Allocation Table/Long File Name) patent licensing program, where we have 18 licensees to date." This is being done under Microsoft's FAT LFN File System Licensing Program.
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."
Why haven't you heard of this before? It's because Microsoft and the companies that have put these licenses under NDA (Non-Disclosure Agreements). So, while we now know there are at least 18 FAT LFN licensees, we still don't know which companies have signed such deals.
This information is kept secret by Microsoft and these companies are well-aware of the open-source and legal backlash that could result from admitting to these patent deals.
The most important reason why the specifics of these deals are under NDA is that any company doing a patent cross license without covering its downstream recipients, i.e. users, is a direct violation of GPLv2 section 7, and is even more explicitly a GPLv3 violation. In other words, if a company admitted to signing such a deal, it could not legally distribute software or hardware using Linux, licensed under the GPLv2, or Samba the file/print server licensed over the GPLv3.
Behind the scenes Microsoft has been threatening open-source software-using companies over patent issues for many years now. Now we know that some of these companies, when they say that company so and so agrees to cross license Microsoft patents without any further detail, we now know that some of these companies are violating Linux and other open-source software licensing.
By doing this Microsoft gets direct revenue from some open-source projects. The additional license fees also increases the cost of commercially supported open-source programs.
Microsoft has essentially been giving companies a choice: pay us under the covers, and violate the GPL, or don't pay and risk a lawsuit.
Now, thanks to TomTom's resistance, Microsoft has been forced to admit that they've already been selling patent protection to open-source using companies. Regardless of how the Microsoft/TomTom case turns out, this is something that open-source companies and non-profit organizations must address. These continuing and blatant violations of the GPL cannot be allowed to stand.