Google has opened a "resource centre" website where its advertisers can learn more about click-fraud.

Many consider click-fraud a potential threat to the company's main source of revenue: pay-per-click advertising.

The new Ad Traffic Quality Resource Center gives advertisers a single place to find Google's information about the problem, said Shuman Ghosemajumder, business product manager for trust and safety at Google.

In the pay-per-click format, advertisers pay every time someone clicks on their ads. Click-fraud can mean companies clicking on competitors' ads to drive up their ad spending, or web publishers clicking on their sites' ads to increase commissions.

With some organisations estimating click-fraud at over 30 percent in general, Google has gone on the offensive, stating publicly what it is doing and what is the extent of the problem in its own ad network.

For example, Google monitors its network for what it calls invalid clicks, which include not only malicious clicks but also innocent practices that may look like click-fraud, such as clicking on an ad twice.

It has concluded that less than 10 percent of clicks on Google ads are invalid, and that only 0.02 percent are declared invalid as a result of advertisers' complaints.

Along the way, Google has locked horns at times with companies that provide click-fraud monitoring and measurement services, questioning the validity and thoroughness of their methodologies.

Originally slated for March, the resource centre's debut last week was delayed as a result of shifting priorities within the group in charge of click fraud, Ghosemajumder said.

For example, the group decided to prioritise a click-fraud forum for Google advertisers that was held at the company's headquarters in May, he said. A similar event will be held later this month in Google's New York City offices, he said.

Already in place is a service called IP Filtering, which lets advertisers "blacklist" certain Internet Protocol addresses for suspicion of click-fraud or simply because their clicks never lead to a sale, he said.

In mid-2006, Google began reporting to advertisers the number of invalid clicks to their campaigns, as well as what percentage they comprise of all clicks.

Google plans to beef up these reports with the amount of money Google didn't bill the advertiser by detecting and discarding invalid clicks. This was also slated originally for March.

Click-fraud has led advertisers to sue Google, Yahoo and other providers of pay-per-click ads. Google reached a landmark settlement of a click-fraud class action lawsuit last year which many described as a big victory for the company. A loss could have likely cost the company hundreds of millions of dollars, but instead Google managed to settle the case for $90 million.

As part of the deal, all but several hundred Google advertisers forfeited their right to sue the company over click-fraud instances dating back to 2002.

The settlement also allowed Google, which admitted to no wrongdoing or liability, to only pay a third of the settlement in cash - all for plaintiffs' attorney fees - with the rest taking the form of credits for advertisers.