FINDING BACKDOORS!!!!!

Hello fellow gmoddersit has come to my servers attention that some sneaky little sam has possibley backdoored into the servers stuff. Now we arnt sure and it could be me overreating and acting like a primary school overprotective mother or maybe not. Just asking if anyone has good idea of ways to check for backdoors where to look some signs of backdoors etc. Yes we have Cac and other basic anticheats. but they are far from perfect

Cheers legends!