this is the CoD4 section, i will move it to mw2 help section
/moved
anyways, to awnser your question about VAC.
VAC cannot detect every single hack, so allot of hackers are outthere using hacks without having a chance on getting banned. (external esp for instance).
But you also have the detected kind of hacks. After using one of such a hack,
you will get banned within 2 weeks. VAC does never peform instant bans.
Dont flame my spelling here, im really tired xD
i hope i explained myself well to you, if not, feel free to pm/vm me.
/marked as solved