going through textures

Being an admin, in fact, today vanish, watched the players going through textures on a secure server. Any ideas?

VAC ban yourself. You'll get no help to catch hackers here.

idiot, ive not want to catch...i want to know - HOW?

One of my friends can do that because he doesn't even see them. We are (me and my friend) part of the staff on a server. We visited an admin's home and he wasn't able to see the house and just walk through everything but I could see it. I think it is just a bug, not hacking.