I'm not so sure how this is done... But I know that an altered map can be used by one player to play alongside the original map used by other players. I suggest MD5 hash checking. It would be an option that the server would have to turn on (by default, on) and would run a pure server. Every Soldat file would be MD5 hashed on the server, and the server would check the MD5 hashes of the client's files. If anything doesn't match, an "unpure client" would be detected, and that player would be ejected from the game.

I don't know if there's a system like this in place, but from what I've read here in the forums, it's obviously not extensive enough.

I want serverside maps, would kill this and maps without custom gfx you wont need to download to play.

the protection is the best i have ever seen
but the [:-censored]ing editor