A little bit more of an explanation of the error and consequences: http://gamrfeed.vgchartz.com/story/85554/garrys-mod-creator-...

tl;dr "Reports were ... flooding in about an error message upon booting up Garry's Mod which reads "unable to shade polygon normals" followed by a bunch of numbers.

The thing is that those numbers that appear after the error is actually the user's SteamID. ...The SteamID...has allowed for easy permanent ban distributions"