How Regular P2P Works
In P2P networks such as Gnutella, your request for a file is broadcast to your immediate neighbour, who passes on the file to his neighbour and so on, until someone who has the file is found. The response, which indicates who has the file, propagates back along the same path. You then download the file directly from the person who has the file.
This system is hard to shut down because there is no central server. Also, all the responsibility for the download of a file rests with the downloader, because the uploader doesn’t know who is going to download the file-he just said he had it! It’s something like having a library and leaving the door open-no-one can prosecute you if someone comes in and takes something!
How BitTorrent Works
You click on a .torrent link, which contains information about a server called a “tracker.” The tracker has information about who has what parts of your file-these people make up a “swarm.” In the swarm is at least one “seed”-someone with the entire file. Some people get parts of the file from one or more seeders, and the process begins.
You begin downloading simultaneously from several peoples’ computers, at the same time uploading parts of what you’ve downloaded to others in the swarm. This happens because different people in the swarm have different portions of the file. You’re now part of the swarm! Ultimately, everyone in the swarm will have the entire file.
The trackers cannot be prosecuted because they do not know the contents of the files they are tracking, and neither do they go about finding the seed-it’s the seed that registers with the tracker!