dissapearing mp3s
 

please help!
after a few months of peaceful existence on my harddrive, EACH AND EVERY mp3 i've downloaded through limewire will eventually truncate - meaning that when i go to play them through my itunes they've suddenly shortened- sometimes only to the first 30 seconds of the song.
this doesn't happen with music i digitize myself, only witht he stuff i'v gottne through itunes.
what on earth is going on?
is there some kind of spyware on my machine that is truncating these files after a term?