PunkBuster has been deployed by several popular multiplayer online games. Some of these games are the Battlefield series, F.E.A.R., Call of Duty series, Quake III Arena, War Rock, among many others.
Pnkbstra.exe stands for PunkBuster Online Gaming Anti-Cheat Automatic Update Service. This background service’s role is to update the PunkBuster anti-cheating software which many games come pre-bundled with. The game cheat used by the player is usually referred to as “Punk” by the PunkBuster terminology.

If you don’t play any games or you uninstalled them, then you can safely disable this service on the Services tab by clicking on Start -> Run in the taskbar, type in msconfig in the open file field and press Enter. From the window that pops up, in the Services Tab you can search in the list of services and disable PunkBuster. This will ensure that it will not start with your Windows, and if you want to run the service, you will have to open it manually.

If you do play games on the PC in question, then it is recommended that you leave this service alone as terminating it will result in the PunkBuster components not getting the chance to update themselves and therefore falling out of sync with the PunkBuster enabled game servers you connect to. This will result in you getting kicked out of game servers which have the latest version of PunkBuster running. This background service uses between 3 to 6 Megabytes of memory. PnkBstrA.exe is considered to be a legitimate file. However, there are a few known cases where problems have arisen out of this process.

The following link is a program and click Uninstall when you run it:

http://www.evenbalance.com/downloads/pbsvc/pbsvc.exe

This program will remove the PnkBstrA.exe and PnkBstrB.exe services. Also you can remove PnkBstrK.sys which is located in C:\Windows\System32\Drivers folder.