>For anyone unfamiliar with WoW, private servers have been a thing for most of WoW's history. It's unclear to me where the source code came from. I've heard different stories (eg from Chinese servers) and also that it was a greenfield development reverse-engineered from the client. All of this was a copyright violation of course and Blizzard have shut down such servers in waves.

It was explained to me, a long time ago, that WoW's traffic was originally unencrypted and a lot of it was reverse engineered from packet captures. Thats now roughly a standard and while people cant sniff modern games, they can just go back to the old mechanics and the old netcode clones are still good.

That was something an old WoW guy told me while he was setting up a local WoW server in college but it feels good.