Google is to introduce a new service to its AdWords advertisement management service in April that allows clients to block certain users from seeing their ads.

The move will allow advertisers to further combat click fraud, a phenomenon in which website operators click on ads on their own websites to boost revenues, or click on online ads for their competitors to deplete their marketing budgets.

Controlling who is presented with the advertisements allows a company to prevent them from being seen by competitors.

Click fraud is considered the Achilles heel of pay-per-click advertising. When advertisers are no longer able to rely on the accuracy of the billing system, they are likely to lose faith in the service.

"Ultimately, the biggest benefit of the pay-per-click advertising model is that advertisers can measure the performance of their campaigns extremely accurately," Google stated on a company blog.

"Thus the most important metric that our advertisers and Google are focused on is providing the best possible return on investment."

Google claims that less than 10 per cent of all clicks on its ads are fraudulent, representing roughly $100m in annual advertising fees which are not invoiced.

The company is able to filter out most of these clicks automatically and conducts proactive analysis to weed out any additional false clicks.

Advertisers can also report clicks which they believe have slipped through the filtering system. Google claims that clicks detected this way represent less than 0.02 per cent of all clicks, or $200,000 per year.

The Internet Advertising Agency is currently working on industry standards on click fraud to provide accepted definitions of a fraudulent click. The group's representatives include Ask.com, MSN Search and Yahoo.