Back in 2005-2006, I was a moderator of a lobby-based doom engine program called Doom Connector. When you get banned, a registry entry was made to prevent you from logging in again, even if you uninstalled and reinstalled the program, changed your ip, or made a new account.
So what did some people do? Format their hard drive and reinstall windows. There were a few guys who would do this and sign on again just about every week and try to troll.. just to get banned within seconds.