In the context of software-patent litigation, open-source licenses are generally an afterthought during discovery, if they are considered at all. By failing to consider their opponents' use of open-source licenses, however, accused infringers may be missing out on opportunities to discover key facts that could open the door to new litigation strategies. For example, there may be situations where an accused infringer may be able to limit damages, raise new defenses, or file counterclaims because an opponent licensed software under an open-source license or used open-source software. This may be especially true when the open-source license in question is the GNU General Public License (GPL) version 3, or GPLv3.
The GNU GPL is one of the most common licenses for open-source software. The most recent version of the GPL, GPLv3, contains express provisions related to patent licensing. For example, licensees are granted a royalty-free patent license to "essential patent claims" of the licensor—patent claims that would be infringed by making, using, or selling the software if there were no license in place. In addition, licensees may not impose a license fee, royalty, or other charge for patent rights granted by the licensor to downstream recipients under GPLv3. Other provisions prevent licensees from engaging in practices pertaining to discriminatory licenses.