Fortune Magazine has an article in which Microsoft General Counsel Brad Smith, and licensing chief Horacio Gutierrez assert that free and open source software ("FOSS") such as Linux infringe 235 Microsoft patents. More specifically,
[Gutierrez] says that the Linux kernel - the deepest layer of the free operating system, which interacts most directly with the computer hardware - violates 42 Microsoft patents. The Linux graphical user interfaces - essentially, the way design elements like menus and toolbars are set up - run afoul of another 65, he claims. The Open Office suite of programs, which is analogous to Microsoft Office, infringes 45 more. E-mail programs infringe 15, while other assorted FOSS programs allegedly transgress 68.
Another controversy worth watching.