Valve Anti-Cheat
Developer(s) Valve Corporation
Initial release 2002
Development status Active
Operating system Windows XP and later, OS X, Ubuntu (beta)
Platform Microsoft Windows, Linux
Type Anti-cheat software
Software license Proprietary
Website Valve Anti-Cheat (VAC) System - Steam Support

Valve Anti-Cheat, abbreviated to VAC, is an anti-cheat solution developed by Valve Corporation as a component of the Steam game development platform, first released with Counter-Strike 1.6 in 2002. During one week of November 2006, the system detected over 10,000 cheating attempts.[1] As of 2012, it is estimated that over 1.5 million Steam accounts have been banned by VAC.[2][3] As of 2013, it is used in over 60 games on Steam.

When the software detects a cheat on a players system, it will ban them in the future, possibly days or weeks after the original detection.[4] 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.


In 2001, Even Balance Inc, the developers of the anti-cheat software PunkBuster designed for Counter-Strike and Half-Life mod stopped supporting the games as they had no support from Valve. Valve had also rejected business offers of integrating the technology directly into their games.[5][6]

Valve started coding on a 'long-term solution' for cheating in 2001.[7] VAC was first released with Counter-Strike 1.4 in 2002, during its initial release, it only banned players for 24 hours.[8] The duration of the ban was increased over time, players were banned for 1 year and 5 years, until 2005 when any new bans became permanent.[9] The initial version, VAC1, saw success for a period, but in March or April 2004 updates ran dry as the Valve engineers maintaining it moved on to the production of its successor, VAC2.

During the early testing phase in 2002, some information was revealed about the program via the HLDS mailing lists. It can detect versions of "OGC's OpenGL Hack", OpenGL cheats, and also detects CD key chaners as cheats. Information on detected cheaters is sent to the ban list server on IP address on port 27013.[10] There is also a 'master ban list' server. The port was later changed to 27011.[11][12] RAM/hardware errors detected by VAC may kick the player from the server, but not ban them.[13][14]

On November 17, 2006, they announced that "new [VAC] technology" had caught "over 10,000" cheating attempts in the preceding week alone,[1]

As of 2012, unofficial sources estimate that over 1.5 million Steam accounts have been banned by VAC.[2][3]

Eric Smith and Nick Shaffner[15] was the original contacts for game administrators. In February 2010, the VAC Team consisted of Steam's lead engineer John Cook and his team of 16 engineers.

The software sends client challenges to the machine, if the appropriate response is not received, it is flagged as a possible violation.

It uses heuristics to detect possible cheats when scanning the computers memory, an incident report is created whenever an anomaly is detected, which is then analyzed by Valve's engineers. The engineers inspect the code and may also run it on their own copies of the game. If the code is confirmed as a cheat, it is added to the database of cheat codes. New detections are also compared to previous detections in this database.

According to Steam's lead engineer John Cook, to stop the anti-cheat software itself from being exploited, "The software is constantly updated and sent down in small portions for the servers as needed, so hackers only get to see small portions of it running on any particular time. So while they may be able to work around pieces of it, they can never hack everything."[16]

Valve also accepts submissions of cheat programs and cheat websites from players through the official Steam Forums. Players may also report players they suspect of cheating through their Steam Community profile, although players are not banned from these reports alone.[17]


  • Total integration through Steam, including using the Steam framework for any update tasks.
  • Delayed bans deny cheat producers accurate and timely information. This causes a reduction in the supply of cheat programs to players who want to cheat online.



A material hack, a type of content hack that VAC2 does not detect.

  • VAC does not detect 'content hacks', where, for example, texture transparency and color are manipulated, since they do not involve modifying any program code. In Source engine games the option to create "pure" servers (sv_pure) that prevent custom content from overwriting the game's defaults was created to alleviate this.[18] Although this does not apply to Call of Duty: Modern Warfare 2 & Call of Duty: Modern Warfare 3, which does not allow the editing of any game files except config files.[17]

Delayed bans, criticism and rationaleEdit

If a cheat is found the player's Steam account will be flagged as cheating immediately, but the player will not receive any indication of the detection. It is only after a delay of "days or even weeks"[4] that the account is permanently banned from "VAC Secure" servers[17] for that game, along with other games that use the same engine. (e.g. Valve's Source games, GoldSrc games, Unreal engine games). Valve never discloses which cheat was detected.

False-positive detectionsEdit

There have been allegations that VAC has banned users for false positives.

  • There are six recorded instances of incorrect detections, which were fixed and rescinded:
    1. VAC1: On its initial release, VAC would issue bans for faulty memory. Valve quickly updated VAC to only kick for faulty memory.[19]
    2. VAC1: Running a VAC-protected game through the Cedega software compatibility layer for Linux.[20]
    3. VAC1: An apparent server-side glitch on April 1, 2004.[21]
    4. VAC2: Over two weeks in July 2010, approximately 12,000 owners of Call of Duty: Modern Warfare 2 were banned when Steam updated a DLL file on-disk after it had been loaded into memory by the game. Those affected received a free copy of Left 4 Dead 2 or an extra copy to send as a gift.[22][23][24]
    5. VAC2: In January 2011, owners of Call of Duty: Modern Warfare 2 or Call of Duty: Black Ops were banned due to their computers being infected by the trojan Win32/Spyeye.H.[25]
    6. VAC2: In June 2011, an unknown false positive detection caused a handful of Team Fortress 2 owners to become banned.[26]
  • There are four recorded instances of game plugins that are not considered cheats triggering bans. These are:
    1. VAC1: HLamp, which allowed the user to control Winamp from the game's interface.[27]
    2. VAC2: The X-Spectate tool, which allowed server administrators to enable a translucent wallhack effect while spectating to help decide if another player was doing the same. Later downgraded to a kick from the server, but bans not rescinded.[28]
    3. VAC2: Some Half-Life modifications, such as Paranoia[29] and Half-Life FX which made changes to the engine's renderer that propagated to multiplayer games. This still triggers a ban and no bans caused by it have been reversed.
    4. VAC and VAC2: sXe Injected, an anti-cheat system for Counter-Strike.

Cheats may be hidden inside otherwise legitimate mod or skin downloads that are created to maliciously get innocent people banned. Since the source of a cheat installed on a computer cannot be proven, bans due to this are never rescinded.[4]

Valve has "a zero-tolerance policy for cheating and will not lift VAC bans under any circumstances."[17] This includes account hijacking and other circumstances beyond the control of the account's owner.

Manually applied bansEdit

In July 2010, several players who successfully used information leaked from Valve to increase their chances of finding a rare cosmetic Team Fortress 2 item called the Golden Wrench found themselves banned by VAC.[30][31]

Games that support VACEdit

The following games use VAC:[32][33]

Mods based on the games above may inherit VAC support from the host game.

dagger Denotes GoldSrc games, if a player is banned in one of these games they are banned from all of them.[17]
double-dagger Denotes Source engine games, if a player is banned in one of these games they are banned from all of them.[17]
Hash-tag Denotes games that have a stricter policy of having all servers VAC protected, and additionally bans players for editing of any game files except config files.[17]

See alsoEdit


  1. 1.0 1.1 "Steam Message". Steam Update News. November 17, 2006. Retrieved December 11, 2002.
  2. 2.0 2.1 "gameME - Make gaming competitive! - Bans". TTS Oetzel & Goerz GmbH. 2 January 2013. Retrieved 2 January 2013. "VAC: 1,573,554 Players"
  3. 3.0 3.1 "See the VAC status of any Steam account (Counter Strike, Left 4 Dead, Call of Duty: Modern Warfare 2, etc)". Surian and AnAkIn. 2 January 2013. Retrieved 2 January 2013. "Total Banned: 1,574,544"
  4. 4.0 4.1 4.2 "I've Been Banned". Valve Support FAQ. January 23, 2008. Retrieved September 18, 2008.
  5. "Punkbuster to stop HL/CS development".
  6. "Punkbuster Retires From HL".
  7. "Eric Smith, Valve, HLDS mailing list, October 2001".
  8. "Online cheaters face games ban". BBC News. August 29, 2002. Retrieved August 23, 2006.
  9. "VACBanned - Information".
  10. "Eric Smith, Valve HLDS Mailing List, July 2002".
  11. "Eric Smith, Valve, HLDS mailing list, August 2002".
  12. "Eric Smith, Valve, HLDS mailing list, February 2003".
  13. "Eric Smith, Valve, June 2003".
  14. "CS-Nation".
  15. "CS-Nation-the future of Coutner-Strike".
  16. "Steamed: Valve Software Battles Video-game Cheaters".
  17. 17.0 17.1 17.2 17.3 17.4 17.5 17.6 "Valve Anti-Cheat System (VAC)". Steam Support. November 15, 2006. Retrieved December 23, 2006.
  18. "Pure Servers". Valve Developer Community. June 6, 2007. Retrieved July 11, 2007.
  19. "VAC Update". SK Gaming. June 18, 2003.
  20. "WineX and VAC". CS Nation. July 10, 2003. Archived from the original on May 28, 2006. Retrieved July 28, 2006.
  21. "VAC Bans Ramp Up". CS Nation. April 15, 2004. Retrieved July 28, 2006.[dead link]
  22. Smith, Quintin. "Valve Anti-Cheat software goes a bit GlaDOS?". Rock, Paper, Shotgun. Retrieved July 26, 2010.
  23. "Valve offers free game after 12,000 false Steam bans". GamesIndustry International. July 27, 2010.
  24. Kubba, Sinan (September 21, 2012). "Joystiq".
  25. "Re: Told You So !!!!". Valve Software. Archived from the original on February 28, 2011. Retrieved March 4, 2011.
  26. "For those hit by the recent ban wave over the past two days". Valve Software. July 1, 2011. Retrieved July 2, 2011.
  27. "HLamp".
  28. "X-Spectate and Admin ESP*".
  29. "Mod DB - Paranoia".
  30. "TF2 Engineer Update Gets Serious – VAC Bans Issued". DeviceMAG.
  31. "Golden Wrench Scandal – Team Fortress 2 Golden Wrench Stolen". Top Tier Tactics.
  32. "Steam games with VAC".
  33. "Valve Announces New Free Game: Alien Swarm".

External linksEdit

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