PnkBstra.exe - This process is associated with the PunkBuster anti-game cheat program for online multiplayer games. PunkBuster is installed with games such as Battlefield 4 and Far Cry 3 and is mandatory to play online multiplayer games. For further information click the link below: http://evenbalance.com/index.php
This is usually detected as malware but if removed will affect the games installed especially when online.
Non-system processes like pnkbstra.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that over time your registry suffers fragmentation and accumulates invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues