Client_test – what file sharing tracking looks like?

client_testClient_test – what file sharing tracking looks like?

Ever wondered how they send copyright notices to people who illegally download a movie or TV show?

Basically, a tool is used that joins a torrent swarm, but does not download the files. It checks connectivity to every peer and possibly also takes into consideration how much of the infringing material a person has downloaded.

A very interesting article from 2002 can be found here:

Pretty old, right? Well, the software BayTSP is still being used nowadays. In some torrents you can see a peer with the client “client_test/”. Of course this may vary.
If your torrent client resolves IP addresses, you should see something like “”. Sometimes the resolving address may also be “*” (* being a wildcard). is only their hosting provider, so this may change over time (redirects to



However, it always seems to use Port 6881.

The most interesting part of the article from to me is the following:

“All we do is go to the same places any user could go, look at the same files anyone else could look at, and we only probe the ports on yourcomputer that you have made public.”

This could in fact mean that tools like Peerblock, which stops known IP addresses from file sharing hunters from connecting to you, actually have an influence on if you receive a copyright notice from your provider or not. These tools mostly use the bluetack blocklist, which unfortunately is pay-only now.

You could also simply delete the torrent if you see BayTSP in your peers list. I doubt it connects to all peers every second, more like every five minutes.


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