"Conventional wisdom among free software and open source developers has long warned that software patents could corrupt and disrupt good software projects. The GPL mentions such a risk, for example. While only a few patents have actually stopped the development of some software (Unisys' GIF patent, the patented LZW algorithm, and Fraunhofer's MP3 patent), the risks involved in developing software in a patent-haunted world remained unclear.
Though many developers prefer to ignore patents, the current laws (at least in the U.S.) provide minimal legal defense for unwitting infringements. Worse yet, though a project may have pedigreed and documented prior art that could easily convince a court to overturn a patent, the cost of such an action is out of reach for most developers -- and many companies.
A recent report commissioned by Open Source Risk Management (OSRM) examined the Linux kernel for patent violations that patent holders could cite in lawsuits against distributors. Unsurprisingly, the report found 283 patents that might come into play."