I haven't run into that particular problem yet, but I'd be willing to bet the farm that it's done by the record companies.
I have had one incident where a song I downloaded said "Property of MCA Records" all the way through the song. Hehehe.
I really can't blame them too much. I mean...I know I probably abuse the p2p thing sometimes and the artists really do deserve to get the loot from those tracks.
I understand checking out some songs to see if you wanna buy the album. But it's so easy to just rip off a copy and not think twice about it.
Uhhh...did I just babble a little? Sorry.
It happens sometimes.