Google always detects your click fraud on Adsense pages. I know many prsons who always say after getting banned from google adsense that what we have done? We have never click on our own ads? we have never gave any incentive to click on ads. But they know that they have duplicate accounts and they do not know that google can detect their fraud with following methods.
The web pages you visit: Google AdSense is used by many web pages for online advertising, and Google's cookies record your visits to web pages with their ad program on them. They have very intelligent bots that are monitoring your activity all the time. These will monitor if you visit any hidden or click incentive pages. Then you will get banned soon.
The blogs you read: If you use Google Reader, Google knows the blogs you subscribe to. Even if you're not on Google Reader, Google knows all of the Blogger pages you visit.
Who and what you're emailing: oops. You are can be caught up by google when you send an e-mail to any preson. Google knows this by gmail that to whom you are sending a message, what will he do.(May be a click request). Google will take action quickly.
What's on your PC: If you're using Google Desktop, Google knows everything that you keep on your computer.
Your schedule: Google Calendar opens your personal and business schedule up to the prying eyes of Google.
Your social network and interests: Google indexes sites like Orkut, Facebook, and Digg, and as such, has access to information about what you're interested in online.
Where you and your friends are: Using Google Latitude, cell phone users can share their location with others. Even if you're not using Latitude, Google Maps for mobile can approximate your location.
Your medical issues: Do you use Google Health? If so, you're sharing your entire medical history with Google.
Mobile number: On SMS, Google Mobile, and Gmail, you can reveal your mobile number to Google.
What you, your friends and family look like and do: With the photo editor Picasa, you're revealing your photographs, friends, and moments to Google.