Modern P2P are distributed systems, there's no central to be located or shut down, >P2P don't download files from a single user, the files are downloaded in chunks and in some cases you can have downloaded your file from 1000 users. Each of those "chunks" had data as to where it came from and to where it is going. With data mining software, plowing through all those "chunks" will give the user of that software a map of any P2P network. It's just a matter of how badly they want to shut them down.