White diagonal line across screen

After entering the Help & Support section, I quickly noticed that I am not the only one with this issue. (http://forum.facepunch.com/showthread.php?t=1315436)

There is a white diagonal line running across my screen. This just started today. It turns on when someone is picking something up with a physgun, freezing a prop, and unfreezing a prop (Unless the halos for those effects are turned off, in which case the white line does not appear.) The white line appears when a halo is drawn.

Also, skies are glitched out:

Flatgrass sky:

Ocean_Evening sky:
(The sky is different on this map, and as such is not glitched out. However, the water is glitched.)

Freespace 13 sky:

Anyone have any idea what’s going on?

The other guy with this issue did it too, so I’ll post my specs if it means anything:

Intel i7-3610QM
GTX 660m
Win. 7

you are missing game content. IE Counter Strike Source

But the problem only started yesterday, and I didn’t have the content before then either. Also, that doesn’t really explain the white line across the screen…

[editline]15th October 2013[/editline]

Aha. I solved the problem. Avast had put some gmod shader dll’s in my “Virus Chest.” No idea.