Big issue, files getting deleted or changed

Hello,
yesterday the files in our ulib data folders had been made to be called “o.txt” with the contents as “lol”, we fixed that,
and today i looked at the server and the files in the gamemode had been deleted along with the whole data folder and several other things,

i dont know what the hell is happening, we have ftp secured, and keep people away from many commands that they could exploit, it seems
they have been using backdoors and exploits from what several friends said, im just about to put this code in to stop file.Delete and such, hopefully it will fix it.

function file.Delete(path)
Msg("Script kiddie tried to delete: " … path … “.”)
end

function file.Remove(path)
Msg("Script kiddie tried to delete: " … path … “.”)
end

Think this will help?

No. This is a source engine exploit. You could try to put sv_allowupload to 0.

Is this the only method of preventing it or is it the only one that wont reveal how it works?