If you have access to server logs, try search player connections that name contains like "dvs" etc, etc.
When you get the impostor login, you get the smurfs too and you get the IP also and with that Ip you can search the same IP range of other players to know the real name of impostor.
In our forum, there are a post of a player who have taken many smurfs of us:
http://foros.cerolag.com/f-enemy-territory-quake-wars-273/t-un-player-nos-esta-robando-los-nombres-como-smurfs-67586.htmlAdd a new fake : SardinetteOu
Fake : SardinetteOu is SewcioPL
Fake : SardinetteOu is BlueRed and Falcon.PL
Fake : SardinetteOu is Premrznan and www
Fake : SardinetteOu is rippeacheap and -lucifer-
Fake : SardinetteOu is CabezaCruda and yyyyy
Fake : SardinetteOu is XTMBZ and vasabi1