I read an interview with one of the manager on Steam VAC. He said he could not say how VAC works in detail, but they analysed primarily 3 things:
* The first thing they check is the values of the game to see if there are unexplained changes (such as spikes or drops such and such values). For example: + 999999 extra money.
* The second thing they check have trophies or awards. They check if the trophies are obtained in order and if they are attainable for a normal player at certain points of the game.
* The third thing they check is specific to cheathappens.com (I think). They analyze the online authentication trainer when you activate it. When you activate the trainer in online mode the software check to see if you are using your specific trainer. They check this trace, this link to detect you .
I hope this message will help cheathappens and their team. Besides, if Wizard, Caliber and 0x90 could take a look at this post I think will be good.