PunkBuster is a computer program published by Even Balance, Inc. Its purpose is to prevent cheating in online games by banning players.
It has been deployed in several popular multiplayer online games, including the Battlefield series, America’s Army, Crysis, F.E.A.R., Medal of Honor series, Call of Duty series, Quake III Arena, Joint Operations, War Rock, and others.

History
Tony Ray founded Even Balance to develop PunkBuster after his experience with cheaters on Team Fortress.
The first beta of PunkBuster was announced on September 21, 2000 for Half-Life. Valve Software was at the time fighting a hard battle against cheating, which had been going on since the release of the game. The first game in which PunkBuster was integrated was id Software’s Return to Castle Wolfenstein.

Features
Published features
· Real-time scanning of memory, a feature also prominent in many spyware programs, by PunkBuster Client on players‘ computers searching for known hacks/cheats using a built-in database.
· Throttled two-tiered background auto-update system using multiple Internet Master Servers to provide end-user security ensuring that no false or corrupted updates can be installed on players‘ computers.
· Frequent status reports (encrypted) are sent to the PunkBuster Server by all players. When necessary, the PunkBuster Server raises a violation which (depending upon settings) will cause the offending player to be removed from the game and all other players to be informed of the violation.
· PunkBuster Admins can also manually remove players from the game for a specified number of minutes or permanently ban if desired.
· PunkBuster Servers can optionally be configured to randomly check player settings looking for known exploits of the game engine.
· PunkBuster Servers can be configured to instruct clients to calculate partial MD5 hashes of files inside the game installation directory. The results are compared against a set configuration and differences logged, and optionally, the client removed from the server.
· PunkBuster Admins can request actual screenshot samples from specific players and/or can configure the PB Server to randomly grab screenshot samples from players during gameplay.
· An optional „bad name“ facility is provided so that PunkBuster Admins can prevent players from using offensive player names containing unwanted profanity or racial slurs.
· Search functions are provided for PunkBuster Admins who wish to search player’s keybindings and scripts for anything that may be known to exploit the game.
· The PunkBuster Player Power facility can be configured to allow players to self-administer game servers when the Server Administrator is not present entirely without the need for passwords, in which the players can call votes to have a player removed from the server for a certain amount of time.
· PunkBuster Servers have an optional built-in mini HTTP web server interface that allows the game server to be remotely administered via a web browser from anywhere over the Internet.
· PunkBuster Admins can stream their server logs in real time to another location. Non-profit organizations like Anti-Cheat Inc., Airdale Ops Network , PunksBusted , PBBans and AASA are examples of groups that use this feature to create shared banlists for their members.
· PunkBuster has initiated Punkbuster Hardware Bans, that bans hardware components upon detection of cheats that disrupt or circumvent PunkBuster’s normal operation.

Unpublished features
· PunkBuster scans for unknown exports (APIs) in sensitive software such as graphics libraries. Upon finding an undocumented export a violation is raised and the client removed from the game.
· PunkBuster does not allow Windows users without administrative accounts to connect to any games. Upon connecting to a game, the user will be immediately kicked for having insufficient OS privileges. Starting with PB client v1.700, a windows service with full administrative rights is used in complement with the ingame PunkBuster client, allowing updates without user rights elevation.However, some games might still require administrative rights before PunkBuster will function correctly.

Incompatibilities
People using overclocking or tweaking programs have complained of instabilities with PunkBuster. For example, both ATI Tool and Rivatuner have incompatibilities. However in newer versions of Rivatuner there is an optional countermeasure.
Some games (like Crysis) do not have a 64-bit version of PunkBuster. For this reason, 64 bit clients will not be able to play in PunkBuster enabled servers, unless they run the 32-bit client of the game.

Enforcement
Global GUID bans and Hardware bans
PunkBuster incorporates a system called global banning. Either the GUID (generated from the CD key) or parts of the computer hardware are banned from PunkBuster enabled servers. Most cheats simply will get a detection, but cheats that interfere with PunkBuster’s software could get a global GUID ban. This will disallow access to PunkBuster enabled servers for that particular game. Cheats which are even more interfering could end up getting the user banned from all PunkBuster enabled games by a hardware ban.

As of June 30, 2004, Even Balance has incorporated the usage of unique hardware identifiers to permanently ban players from all PunkBuster enabled servers who raise a violation that corresponds to hacking or interfering with PunkBuster’s normal operation and therefore violating the EULA.

Even Balance uses multiple private one-way hashes so that no serial number information for individual computers can be determined by admins or anyone else who may try to obtain this information from a hardware GUID.

PunkBuster only gives a hardware ban if memory scans show that a cheat that is known to circumvent or disrupt PunkBuster’s normal operation or its facilities is activated.

As with previous PunkBuster GUID global bans, the new hardware GUID bans are permanent and will not be lifted. Even Balance has not disclosed which hardware parts are used to ban players, but trial and error has shown that the hardware GUID is based on the serial numbers of all available hard drives and the MAC addresses (which can be changed with a simple fix in the Windows registry) of all available network interfaces.

According to their EULA, Even Balance has the final say in matters of banning.

Attacks on PunkBuster
PunkBuster usually searches for known cheat program signatures as opposed to relying on a more heuristic approach. On March 23, 2008, hackers published and implemented a proof of concept exploit of PunkBuster’s indiscriminate memory scanning. Because PunkBuster scans all of a machine’s virtual memory, malicious users were able to cause mass false positives by transmitting text fragments from known cheat programs onto a high population IRC channel. When PunkBuster detected the text within user’s IRC client text buffers, the users were banned. On March 25, 2008, Even Balance confirmed the existence of this exploit, and advised users not to run any other programs at the same time as PunkBuster protected games. However, this advice was insufficient, as crackers started embedding binary strings in their avatar pictures and signatures on legitimate forums, causing people who browsed the forums to be kicked, even after the browser was closed.

Sources: Wikipedia Modified by Fanterazzi