DougV recently posted a cryptic message in the Steam forums regarding VAC (Valve Anti-Cheat) for the Source engine:
"VAC will be here in the not too distant future and will catch a lot of people by surprise."
In other words, good news for fair players; the Source VAC system is believed to be very effective against cheaters.
One could speculate whether the term "A not too distant future", when used by Valve, actually represents a not too distant future, but as the unpleasant events around Half-Life 2's delay (and the causes thereof) are over, this is most probably accurate.
Furthermore, regarding DougV's statement of catching people by surprise, we would advise against using any kind of cheat, or you might end up among the ones to have their accounts abruptly suspended!
News source:
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