Sure, but its not about user agents.

benburton · on Aug 24, 2015

How else would you detect the operating system of the client making the request?

nirvdrum · on Aug 24, 2015

I have no idea if the the trackers are doing this or not, but you could use TCP/IP stack fingerprinting. It's a bit costly, so I doubt it's in use. But it could be one way to achieve it. It's certainly not 100% accurate, but my experience with nmap is the detection works surprisingly well:

https://nmap.org/book/man-os-detection.html

happyopossum · on Aug 24, 2015

That requires the server to be able to make network requests to the host - not gonna happen for most users busting your site.

deno · on Aug 24, 2015

Only if you use nmap as-is. Also majority of torrent software uses UPnP IGD to open TCP port (which is then advertised to the tracker).

I’m not sure but I think µTorrent on Windows also listens on the Toredo provided IPv6 address.

tokenizerrr · on Aug 24, 2015

What do you think it's about, then?