Peers in a bittorrent swarm advertise which pieces of a file they have, it is very easy to see which IP addresses in a swarm have 100% of the data (and thus hav

Peers in a bittorrent swarm advertise which pieces of a file they have, it is very easy to see which IP addresses in a swarm have 100% of the data (and thus have downloaded the complete files). Proving that a particular person downloaded those files is an exercise left to the reader ;)