Truly speaking I really don’t know the way how Google get to know about click fraud

I am trying to figerout how they get know

1>There are very complex methods used by them to study about Invalid Clicks. They use both human and machine research. The exact method used by them is not publicly disclosed.

2>various measures are taken by Google adsense to identifies click frauds. There are search engines which track more than 50 data points, IP address, browser’s information, user’s session info and pattern recognition. And Google has eye on website or forums which has fraud clicks exchange articles etc

3> Think you get 5 visitors, and all 5 click the ads – your ctr (click through rate) is 100% that’s nearly impossible without cheating, it raises flags and If you get 5 visitors, and only 1 clicks the ads – that’s 1/5 20% CTR – which again is suspicious and raises flags. (This is applicable for the publishers who have very less page impressions …like u have 1to 10 impressions per day or 100 to 1000 impressions per month)