The Free Software Foundation, which authored the General Public License and owns rights to much of the code at the heart of Red Hat Enterprise Linux, inserted that clause into the agreement in an effort to discourage other open-source software developers from signing patent deals with Microsoft.

     The authors of that license have said they believe that such patent deals will help Microsoft back claims that its intellectual property is being violated by code in Linux and other open-source software, eventually giving the company ammunition to seek billions of dollars in license fees from users of open-source software.

     Linux is the biggest rival to Microsoft Windows and also the most popular type of open-source software.