ALL THE BIG CAT RED TRUCK DOG

[fredmg77]

ALL THE BIG CAT RED TRUCK DOG

[rogerxiii]

They could have your RCON password, which would be VERY dangerous as it could damage your whole server. I would recommend updating the password and installing SMAC, SourceMod Anti-Cheat, the best anti-cheat plugin there is.
https://forums.alliedmods.net/forumdisplay.php?f=133

EDIT: I just realized you might not have even chosen a password. Add this line into your server.cfg:
rcon_password "PASSWORDHERE"