The Valve Anti-Cheat System (VAC)
Because nobody likes playing with cheaters.
Playing games should be fun. In order to ensure the best possible online multiplayer experience, Valve developed a state-of-the-art anti-cheat system that automatically detects and permanently bans any player using cheats or hacks on a VAC secured server. What this means to you as a player is that you don't have to worry about annoying cheaters getting an unfair advantage and disrupting your game.
The Valve Anti-Cheat system is only enabled on servers with the secured shield logo and only

Ok your're salty because you think I'm hacking. Calm down, take a deep breath and just accept the fact that I'm way better then you. Anyways if you still think I'm hacking just report me and move on. Whatever kid. Oh I'm sorry did I ♥♥♥♥♥♥♥ trigger you? Were you ♥♥♥♥♥♥♥ triggered you little cry baby? ♥♥♥♥ off. Literally saying not a ♥♥♥♥♥♥♥ word to you and you're gonna ♥♥♥♥♥♥♥ mute me because you have a problem with me just ♥♥♥♥♥♥♥ talking ♥♥♥♥ in all chat? Honestly go ♥♥♥♥ yourself to the highest ♥♥♥♥♥♥♥ caliber you ♥♥♥♥♥♥♥ ♥♥♥♥♥♥♥. So sick of little ♥♥♥♥♥♥♥ ♥♥♥♥♥♥♥ like you who ♥♥♥♥♥♥♥ have a ♥♥♥♥♥♥♥ opinion like you're ♥♥♥♥♥♥♥ sitting over there like, oh I'm some ♥♥♥♥♥♥♥ problem to you because I'm not even ♥♥♥♥♥♥♥ saying a ♥♥♥♥♥♥♥ word to you. ♥♥♥♥ off. Call it what you ♥♥♥♥♥♥♥ ♥♥♥♥♥♥♥? Hormonal? Kid you're a ♥♥♥♥♥♥♥ bullshitter. You're a ♥♥♥♥♥♥♥ bullshitter. Go ♥♥♥♥ yourself. You ain't ♥♥♥♥♥♥♥ nothing.