Valve Anti-Cheat

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, and is used in several games on Steam.

When the software detects a cheat on a player's system, it will ban them in the future, possibly days or weeks after the original detection. It may kick players from the game if it detects errors in their system's memory or hardware. No information such as date of detection or type of cheat detected is disclosed to the player. After the player is notified, access to online "VAC protected" servers of the game the player cheated in is permanently revoked and additional restrictions are applied to the player's Steam account.