Here is what they do:
1. They join eDonkey or Kazaa or whatever and share the latest warez...
2. People will start downloading from them.
3. (This is specifik for eDonkey) They rightclick on users names and add them to friends.
4. Display list of files this user shares, and then they have what they need. Users IP-number and a list of files they share. And yes, this is all they need under danish civilianlaw, because AFAIK under danish civilianlaw you are guilty until the judge is convinced otherwise.
There is a minor fix though:
www.emule-project.net This is an eDonkey client that won't reply to a request to send your filelist to another user.