What are some GMod hacks?

I am not starting this thread so I can hack, I just want to learn the power, as my server has been hacked.
I made a thread earlier asking how to deal with a backdoor. My friend says there is no backdoor with this amount of power, so I am sharing what this hacker can do:
He can explode everyone, forcing godded players out of god.
He can play music on your client (got real annoying).
He can make your screen flash in a rainbow color.
He has access to console, even when not in the game.
Here is a video of him hacking my client:https://www.dropbox.com/s/2hb259t7ygjkmr...d.mp4?dl=0
Here is his steam profile:http://steamcommunity.com/id/NibbaFaggot/
The reason I could tell this guy was hacking is because he was the only person never affected by this, he exploded the whole server, and the only person who didn't die in that was him. I restarted the server a couple of times, and banned his steam ID, but he was still accessing console, as he was forcing me to say "!unban <his steamid>".
Does anyone know of the hack that has this power? How do I get rid of this?