<< If it is a virus with a .MP3 extension, how can that hurt? MP3 files are associated with an application, the application tries to interpret the file as MP3 format, and fails. It's not as if the application will decide to run the MP3 as an executable because it doesn't find music. >>
Cranky, it can't hurt it. MP3's are played in such a way that should the data be unplayable(too many "bad" bits via CRC), the player just stops playing altogether. I suppose a buffer overflow is possible, but that would be hard to do considering that there's no limit on the size of an MP3, and players won't go past 320 usually.