Google has launched the Ad Traffic Quality Resource Center, an online "resource center" concerning click fraud, which many consider a potential threat to the search giant's main source of revenue: Pay-per-click advertising. In the pay-per-click format, advertisers pay every time someone clicks on their ads. Click fraud happens when companies click on competitors' ads to drive up their ad spending or when Web publishers click on their sites' ads to increase their commissions. With some organizations estimating click-fraud incidence at over 30% in general, Google has gone on the offensive in researching the topic in question – the resource center is the latest in a series of click-fraud tools Google has been making available to its advertisers.
Google also proactively 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% of clicks on Google ads are invalid and that only 0.02% are declared invalid as a result of advertisers' complaints. Google has also questioned the methodologies of companies that provide click-fraud monitoring and measurement services. As well, Google offers a service called IP Filtering, which lets advertisers "blacklist" certain IP addresses. 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.