A group of Russian programmers have realized, apparently for an elaborate joke,
the provocatory website www.youhavedownloaded.com: such portal, using a crawler technology very similar to the one used by Google to spider webpages, continuously indexes into a searchable public database all IP addresses connected to many famous nodes (so called “trackers”) of BitTorrent-based peer2peer networks.
By retracing torrent files’ data, the automated website is then able to show, in a very simple way, what users connected through such IP addresses are downloading. Accessing the homepage while a BitTorrent client is connected to monitored BitTorrent trackers will show a (more or less complete) list of what a user is downloading using the relevant IP.
Moreover, by inserting a known IP address into the search box, users can see what other people are downloading with BitTorrent.
Leaving aside the obvious curiosities, this initiative uncovers one of the most critical points of the famous BitTorrent P2P network: as every other online distribution network, it has to rely on central nodes – the trackers – that periodically map all IP addresses of users connected, to ease their interaction during download.

Ironically, the technical limitation of having to use a third-party node also helps prevention from illegal use of the BitTorrent download protocol: just closing the tracker, or blacklisting its IPs on a national scale, prevents illegal file-sharing of copyrighted content.

According to such principle, during the last judiciary “ThePirateBay” case in Italy, one of the measures adopted by the judges was the blacklisting not only of the famous search engine for illegal torrents, but also of the IPs where its dedicated trackers operated. Both activities, as per ruling n.49437/2009 of the Italian Supreme Court, are, in fact, illegal and therefore liable in Court, since they help users finding and illegally accessing/spreading copyrighted contents online.

Once again, the “myth” of a secure Peer2Peer network has to face the harsh truth of a system that can easily record and twist every step taken by digital pirates against them.”