Click fraud has been the single greatest enemy of the Pay Per Click advertising model. There has been complaints from advertisers, and some lawsuits about it.

Now, the major web search engines announced plans to work together to quantify click fraud.

Click fraud occurs when online ads are intentionally clicked on, either by Web sites who get paid for hosting the ads or by companies trying to deplete the ad budgets of rivals so they can buy the search keywords themselves and steal the business.

The Interactive Advertising Bureau (IAB) and the nonprofit Media Rating Council said they are teaming with Google, Yahoo, Microsoft, Ask.com, Looksmart and others to form the Click Measurement Working Group.

The group's mission is to establish guidelines for what constitutes valid clicks and invalid clicks on ads. Guidelines can help the industry measure how prevalent click fraud really is. Third-parties who sell click-fraud-combating services to advertisers claim that click fraud rates are as high as 30 percent. Google and Yahoo counter that click fraud rates are minimal.

If click fraud continues, advertisers will pay less than the current rates for advertising. In the end the industry would not be profitable as one will need more clicks to get the same amount of income.