Licensing and patent issues 2

In September 1998, the Fraunhofer Institute sent a letter to several developers of MP3 software stating that a license was required to "distribute and/or sell decoders and/or encoders". The letter claimed that unlicensed products "infringe the patent rights of Fraunhofer and THOMSON. To make, sell and/or distribute products using the [MPEG Layer-3] standard and thus our patents, you need to obtain a license under these patents from us."
These patent issues significantly slowed the development of unlicensed MP3 software[citation needed] and led to increased focus on creating and popularizing alternatives such as Vorbis, AAC, and WMA. Microsoft chose to move away from MP3 to its own proprietary Windows Media format to avoid licensing issues associated with these patents. Until the key patents expires, unlicensed encoders and players could be infringing in countries where the patents are valid.
Reference : http://en.wikipedia.org/wiki/Mp3