There have been few reported decisions regarding the intersection of patent infringement and the GNU Public License version 2 (GPLv2). This post discusses one recent case:
In XimpleWare v. Versata, et al., Case No. 5:13cv5161, U.S. District Court, Northern District of California (San Jose), XimpleWare sued all defendants [Versata, Aurea Software Inc., Trilogy Development Group, Inc., Ameriprise Financial Services, Inc., Ameriprise Financial, Inc., United HealthCare Services, Inc., Waddell & Reed, Inc., Aviva USA Corporation, Metropolitan Life Insurance Company, Pacific Life Insurance Company, The Prudential Insurance Company of America, Inc. (subsequently dismissed), and Wellmark, Inc.] for direct patent infringement and declaratory relief and the Versata defendants for contributory and inducement of patent infringement.
This May decision was very important because it confirms that the structure of the GPLv2 works: Because the GPLv2 is a direct license from the owners of the intellectual property in the software, a violation by one entity in the distribution chain (Versata) does not affect the rights of its customers (the Customer Defendants) unless they separately breach the GPLv2.
The post also notes that helpful guidance regarding compliance with GPL can be found the Software Freedom Law Center publication Practical Guide to GPL Compliance as well as Copyleft and the GNU General Public License: A Comprehensive Tutorial and Guide by Software Conservancy and the Free Software Foundation.