HOW TO: Protect your P2P privacy
[...] -if you use P2P software, and this can include programs that use it for distribution (which may not be immediately apparent to you), whether you like it or not you're putting your IP address and machine on the global invitation list. It doesn't matter that you've got a firewall -- for while it does its job at the protocol and port level, it can't protect you from the applications you run that openly share information about you or your machine.
Such as P2P software. [...]