Dark Atheist

Security researchers are warning that popular media players offered by Microsoft and AOL are vulnerable to attacks that can completely compromise a user's PC. Attack code has already been released for the bug, which has been confirmed in a codec used by older versions of Windows Media Player, made by Microsoft, and in AOL's Winamp. A Symantec researcher has warned that users of other players may also be at risk because the vulnerability itself resides in a commonly used MP4 codec produced by a company called 3ivx Technologies.

source

http://www.theregister.co.uk/2007/12/10/3ivx_mp4_vuln/