"Click fraud," as wikipedia defines it, is a type of internet crime that occurs in pay per click online advertising when a person, automated script, or computer program imitates a legitimate user of a web browser clicking on an ad, for the purpose of generating a charge per click without having actual interest in the target of the ad's link.

A study conducted by Click forensics revealed that click fraud has reached a new high of 14.2 percent in the last quarter of last year. In addition, the average rate of click fraud on 'content networks' was as high as 19.2 percent.

So what do major search engines do to combat click fraud?

To combat click fraud major search engines like Google applies four layers of fraud detection. They are:

1. Automatic detection - this filters clicks from both the search and content networks in real-time with the goal of removing them before their existence is ever shown to the advertiser.
2. "Flagging system" - an automatic process to remove invalid AdSense clicks.
3. "Manual review" - this process has over 2-dozen Google employees tasked with manually reviewing and removing any suspicious AdSense clicks.
4. "Requested investigations" - The fourth and final layer of click fraud detection that falls to the advertiser and 3rd party click fraud detection companies.