A wallhack is a type of game modification or external software that alters the rendering pipeline of the 3D engine. In unmodified CoD2, the engine (a modified id Tech 3 engine) uses a visibility algorithm called PVS (Potentially Visible Set) . This system determines which objects and players should be drawn on screen based on the camera’s angle and physical obstacles.

How the CoD2 Wallhack circumvents this:

The wallhack concept pioneered in CoD2 directly influenced cheats in later Call of Duty titles (MW2, Black Ops, etc.). Today, "wallhack" remains a generic term for any FPS cheat that reveals hidden players, but CoD2 is often cited in reverse-engineering forums as an ideal learning platform due to its simple engine structure.

Because CoD2’s original PunkBuster anti-cheat was discontinued years ago, community-driven solutions emerged: