This is what is VAC ♥♥♥♥♥♥♥♥ is all about!

Valve Anti-Cheat, abbreviated as VAC, is an anti-cheat software developed by Valve Corporation as a component of the Steam platform, first released with Counter-Strike in 2002. During one week of November 2006, the system detected over 10,000 cheating attempts. As of July 2014, it is estimated that over 2.2 million Steam accounts have been banned by the system.

This software could also ban you for griefing or ruining the game for others.