How google detect invalid click?

Will anybody care to share how google detect invalid click which results in termination of the cheaters' account?

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No one really knows. The most common explanation of "invalid clicks" is that you've clicked on your own ads. Google's software would use a number of factors (IP and other things) to determine whether or not this is true.

It's true, Google keeps most of their information to themselves. You just have to make sure you follow their Terms of Service and Policies, especially for how you are allowed and not allowed to drive traffic to your site. The one thing we can know for sure is that they will find out if you click on your own ads. People make the mistake of thinking that a proxy or changing their ip will help them not get caught, but then they make another mistake by logging into their Google account to check their earnings.

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Also many cheaters are reported by AdWords users who track their campaigns and clicks which they pay for.

I dont know how exactly adsense detect invalid click, but that was one of the reason exposed by adsense when closed my adsense account

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