VAC, the abbreviation of ValveAnti-cheat Technology, is a system that automatically detects cheating programs installed on users' computers. If the user's computer is connected to a VAC protection server and a detectable cheating program is installed, the VAC system will prohibit the user from playing games on all VAC protection servers in the future.

VAC system can effectively detect cheaters' signatures. Any unfair changes made by a third party in favor of the player, including any changes to the game core executable files and dynamic link libraries, are classified as cheating or hijacking, and trigger a VAC ban.

Precautions:

Although server administrators can choose to ban certain players, they can't impose a VAC ban on players. VAC blockade is permanent, non-transferable and cannot be transferred or cancelled by Steam customer service.

VAC ban completely prohibits individuals from playing games on Steam's VAC-protected servers. The server administrator may ban the server, but the ban on the server is not as serious as the VAC ban. The valve cannot prevent the server from being banned. The administrator running the server can ban players at will.