Today you see Google Adsense ads on almost every other website on the Internet. These websites do this to generate revenue from these Google Adsense ads to support themselves and hopefully make some profit. The problem arises when a website's owner creates fraudulent clicks for the sole purpose of generating Google Adsense revenue. That is to say they manually click on the links themselves, or through multiple different computers, to simulate different people interested in the advertiser's website.

For example the author of this article uses both of Google's programs to advertise (Adwords) and to generate revenue (Adsense). Google Adsense is an effective form of advertising because it generates the income for website publishers, and it drives traffic to the advertiser's website.

Read more about the most fraudulently used adsense keyword at http://www.symbiotic.com/Adsense_Keywords/adsense_fraud.php.