Some of them are hackers who break the code in the game to find what are called "glitches" (getting outside a map or an invisible hole in a wall) and others use more analog ways of doing it. It brought down SOCOM 3, SOCOM Combined Assault, and now it's Call of Duty 4. What are called "interrupters" are being used more and more, the older the game gets. An interrupter stops the signal of the game for the opposing team, while the team with the interrupter can move into position before the game starts. Then, the switch is flicked again, your team is none the wiser. At least until you lose or it's made obvious. This tactic usually is undetectable because it happens while the game is loading. Sometimes it's right out there - a signal interrupt message will flash on the screen. The team without the interrupter will think it's just a server error and then the game will resume like nothing happened. Except, now you are more likely to lose the game.
It's not very technical, but devastating to online play. Designers spend hundreds of hours making maps as perfect as possible and fun to play at the same time. But with the flick of a switch, all the tactics and planning of a team can be wasted by one cheater. Ultimately, it will make online games like SOCOM: Confrontation or last year's Game Of The Year Call of Duty: Modern Warfare unplayable. Just knowing that whatever game you get could be glitched or interrupted for the other teams advantage makes playing the game seem pointless. Might as well sell the game and move on hoping for the best.
I mention this because I play with a bunch of guys on COD4 and we have a pretty good team. But tonight we played another team that we thought were better. Then the obvious happened, they went too far. They flicked the interrupter switch just a bit too long. A player for the opposing team was able to stab my character dead within seconds of the game start. On the map we were playing, it would have taken him at least 25+ seconds to get to me, but there he was. Now it's ruined. I don't know if I can continue to play a game with such blatant cheating, knowing that the developer of the game will do nothing to stop it.
Sorry COD4, my love for you is dead.