Just so that you are clued in...

Fast Track Network, which encompasses Kazaa and others only hashes the first 3,000 bytes or so of a file, so thus EVEN if the file is verified the AA can dl it and then hex edit the file with crap and then proceed to ul it a million times over on the network and let it spread since they have the bandwidth to do so, this is generally why the screeching starts at 15 seconds or so on mp3's since thats where they have been altered, thus now the FAKE will swarm with the verified due to a shit hashing system which has been the biggest flaw on the network last time I checked. There was talk of upgrades to fix this but I don't know.

As for many of the other networks mentioned, they have much better hashing systems hashing the entire file, thus if someone were to edit the file anywhere it would appear as a different file and would NOT swarm with the original file.