How to protect user from cloning clients usernames

So this is happening more and more where a user comes in the server and somehow changes his name to another users and starts killing the lobby.

Now we have scripthook disabled and steam auth. What can be done to stop this? Anyone else have this happen to them?

You should keep a detailed log of all the “authorizied” players for you’re community and you might have to start IP banning. People can still get around Ip bans but its a start if you have a dedicated server you can set up protections to block proxies and vpn’s but I am not going to get into that you can google and research that.