Scrambledhttps://github.com/ValveSoftware/csgo-osx-linux/issues/566
This was closed at the same time that the aimtux cheat started getting detected. Maybe since vac got linux support cathook started getting detected also, which is why he's now working on catbase.
I got the info mainly from posts by nullifiedcat that were relayed to me. (basically because people thought that linux not having vac was a bit crazy)
I'll admit that I don't have a very good understanding of how VAC actually works, I just assumed that it was a TF2 only thing since its quite often that TF2 gets ignored.
It always had Linux support, but VAC vs hacks is a game of cat and mouse. Valve had many more years of playing that game on Windows, so VAC is much more comprehensive there. On Linux, there's a lot more things you can do to integrate your hacks, so VAC has to catch up to block those strategies. However, that doesn't mean VAC wasn't on LInux in the first place.