I don't think Modern Warfare 2 ever had fan servers. It's the one that infamously had a "boycott" over the lack of dedicated servers (which is different than private servers) because it was all peer to peer multiplayer.
MW2 had many iterations of fan servers. It started with alterIWnet, and ended with IW4X, which was recently shut down by Activision with a cease and desist. Fan modded versions of the game with dedicated servers and a server browser, with known security vulnerabilities like this one already patched out. Thanks to Activision, there's now no way to safely play this game anymore.