You played something while having a cheat program running. There's usually a few weeks delay. Vac is never wrong, but in the chance that it is make a support ticket. They'll also probably not tell you either, but its worth a shot.

Wrong forum.
http://gtm.steamproxy.vip/discussions/forum/9/

You have connected to VAC-enabled servers with a program that VAC has noticed.

The VAC system reliably detects cheats using their cheat signatures. Any third-party modification to a game designed to give one player an advantage over another is classified as a cheat or hack and will trigger a VAC ban. This includes modifications to a game's core executable files and dynamic link libraries.

You can read all about VAC here:
https://support.steampowered.com/kb_article.php?ref=7849-RADZ-6869#whatisvac

Ok. Can I do something to get an un-ban from Steam?

Originally posted by dreawy:

Ok. Can I do something to get an un-ban from Steam?

No.

Keep in mind, all VAC bans are permanent.

Valve has a zero-tolerance policy for cheating and will not lift VAC bans under any circumstances.

Ok. ;( But if I use the same name on my new account can I get a vac-ban directly from Steam again? :/

Originally posted by dreawy:

Ok. ;( But if I use the same name on my new account can I get a vac-ban directly from Steam again? :/

I'm not sure. I had a friend who got banned on 4, if not 5 different accounts because the hack was still on his computer.

VAC will automatically see if you have a known hack on your computer, so make sure you get rid of the program before you play on VAC-enabled servers.

Ok. Thank you for your advices :)

But I have removed/uninstalled all ''cheatingprograms'' from my computer but it still left. (I talking about Cheat Engine) :/ What I gonna do?!

Format and don't use cheats anymore.

Sorry for the "off topic" question, but does VAC detect a cheat (.exe) also if it's not running? Like some different user has the file stored in his account, can someone still get a VAC ban?

No but if any part of the cheat is still in memory, all bets are off.

Ah ok, so it has to be startet. Because in the discussion it always sounds like it just has to be on the HDD.

The problem is, once you install something like that, you do not know what it leaves running in the background.

Originally posted by Silicon Vampire:

The problem is, once you install something like that, you do not know what it leaves running ion the background.

Good point, as always people should check what they install. Thanks for answers.

I can assure you cheat engine is not detected just for having it on the HDD (at least not my version). But as Silicon said,other hacks/cheats/callthemwateveryouwant install stuff running in the background and modifying some core game files will also get you vac banned again on your new account if you use the same files from the same PC.