GameGuard uses rootkits to proactively prevent cheat software from running. GameGuard hides the game application process, monitors the entire memory range, terminates applications defined by the game vendor and INCA Internet to be cheats (QIP for example), blocks certain calls to Direct X functions and Windows APIs, keylogs keyboard input, and auto-updates itself to change as new possible threats surface.
Since GameGuard essentially works like a rootkit, players may experience unintended and potentially unwanted side effects. If set, GameGuard blocks any installation or activation of hardware and peripherals (e.g., a mouse) while the program is running. Since GameGuard monitors any changes in the computer's memory, it will cause performance issues when the protected game loads multiple or large resources all at once.