Modern versions often go beyond just "seeing through walls." They provide an on-screen overlay showing "skeletons" of players, their names, current health, distance, and even the weapons they are carrying.
For years, Call of Duty 2 relied on PunkBuster for anti-cheat. However, official support for CoD2 by Evenbalance (PunkBuster's creator) ended years ago, leading many to consider older public servers a "cheater's paradise" where unmonitored wallhacks are easily found. call of duty 2 wallhack
Infinity Ward eventually released patches (1.2, 1.3, 1.01) that fixed some specific rendering exploits, but they never fully killed the wallhack. The architecture of the id Tech 3 engine was simply too permeable. Introduction to Call of Duty 2 Wallhack ESP