dalek - you have mentioned Limewire which I installed on a friends system for about an hour and then starting marking anything wrong. I say lot of searche's being shown as [][][] (squre's), I think it might be a buffer overflow or some unknown exploit. anyway if you use it and know anything about it please let me know.
I haven't used mine in awhile, but I never experienced what your describing, check out their FAQ maybe you don't have something configured right.

Would also second ©opy®ight suggestion, you would be amazed at who is out there searching for files, almost all of the universities/college's (where most of the downloading takes place I might add), Military establishments (guards with too much time on their hands Lol).....(or bored clerks). Also the usual RIAA, MPAA etc...

Luck...'