There are a lot of legal issues associated with using open source in a software application. Open source code users usually are required to release added or altered code to the public and give a free license to others to use it without many restrictions. Such licenses can require licensees to disclose source code and distribute derivative works royalty-free. Well-known open source licenses include the Creative Commons License, Apache License and Sun Community Source License. Perhaps best-known is the General Public License, now in its third version, which governs Linux, MySQL, and other major software products. It is perhaps also the most feared for its requirement that any source code compiled with any GPL-licensed source code be publicly disclosed upon distribution -- often referred to as "infection."
Many businesses have successfully and profitably incorporated open source code in to their software products, including Google, Apple and Cisco. Until recently, incorporation of open source code into for-profit products seemed to have gone unnoticed, and the requirements to release "infected" code un-enforced. That may be changing, however. Open source code organizations are getting more aggressive about going after abusers - In December, the Free Software Foundation (FSF) filed a copyright infringement lawsuit against Cisco for an injunction based upon the use of open source code in their Linksys products. Stay tuned.