How google adsense to filter the invalid click?

How google adsense to determine the ads which was clicked is valid or invalid(click by a person maliciously or by bot)?

I know a company doing these kind of work.

http://www.adometry.com/

Formerly knows as Cli开发者_如何学编程ck Forensics.

They are extremely secretive about this. However, their overall strategy is that if they think something is not right, like the traffic or the clicks are coming from specific IP addresses or the ratio of click/page impression is too high, they just suspend the user because they don't want any potential fraudulent activities; advertisement is where all their money is made from.