How Google Adsense detects click fraud

Many of webmasters wants to know how Google detects click frauds, perhaps to prevent from being banned. No one right now have the correct answer!. I had (with some of my friends) made two Adsense account and made the tests.

Account Number 1:
The site was accepted! We added the ads, and then I started my self by clicking on the ads. I was the only person that access to this site. So when seeing the Adsense reports, I see that the CTR level is high (80 %) due to the huge number of click and few impression (Ex : 50 impression and 35 clicks). After some days, Google prevent me from being banned. So Google won't delete your account from the first time, but it will inform you! I continue in click frauds and google disabled my account.
Account Number 2:
I have good traffic with this one because of my friends! We made a lot of traffic and page impression and few clicks (CTR = 5 or 8 %) Google Adsense Generate money. After some days we get an email alerting us from click frauds! (Note : We use a fix IP Address)

Conclusion:
How Google detect clicks then:
1/ Google detects CTR and inform (Adsense robots) it's engineers when a CTR reach a high level (25 % for example) for a long period of time. The engineer won't disable the account, it will visit the site and see what's going on and then alert you.
2/ Google detects the IP address of the computer that make clicks and impression (If always the same that made clicks and impression, then something is strange) Google will alert you before any action he will take
3/ The normal CTR is from 2% to 8% max. If you have 2% or less then you adsense need optimization. If you have more than 10% (for a long period, 1 week for example) and you don't make clicks frauds, then try to detect (with google analytics) who is coming to your site and abusing your ads. tell Google (with email) when you found an abusing IP Address.
4/ As your impression and visitors are numbrous as google won't see click frauds (will pass them). If you have for example 5000 page impression daily, Google Adsense won't take care of an abusing IP Address and will block it him self (simply the clicks of this IP won't generate money, so if you have good traffic don't make click frauds because this don't generate money)

I'm not sure of that (In other words it can be not google method to detect click fraud), you'd better make more research if you want to know!.
Afraid from being banned ?
Simply follow yout CTR and all should go well. If you found for example 5 clicks without revenue then those clicks are click frauds (in normal condition 1 click generate 0.28 ot 0.48 $) and also page impression generate up to 1 $ per 1000 impression (not much but good if you have enough money)

Helpful information about Adsense on : www.Ad-sensing.com (it isn't my site)