This is why lots of indie devs sell their game on steams platform so they can leverage steams VAC to stop cheaters from connecting to servers that do vac checks. Find the account thats being a jerk, report their account, studio stops them from connecting to servers, put that all in the eula and tos so its legal.
Thats the issue here, anego didnt want to pay steam to do this for them, they didnt want to pay a programmer to do it in house either. Thats before we get into the moddb allowing source and the mod to not match and a billion other problems there.