How to remove backdoors

Alternatively to downloading shit that might not even be necessary, you can just run gmod open console and type out lua_find and look for specific keywords like if you plan on running a server with ULX, then some keywords would be "ULX", "Adduser", "SteamID" etc etc. nomalua can also be used but in my experience that shit just crashes the game and doesn't work.

Some other tags like HTTP, HTTPGET etc are also a good idea to look for.

If you want it to be easy and simple then go ahead and download one of the backdoor finders that are posted here but I wouldn't count on them yet alone trust.