Pay per click advertising

Pay per click advertising or, PPC advertising, is an arrangement in which webmasters (operators of Web sites), acting as publishers, display clickable links from advertisers in exchange for a charge per click. As this industry evolved, a number of advertising networks developed, which acted as middlemen between these two groups (publishers and advertisers). Each time a (believed to be) valid Web user clicks on an ad, the advertiser pays the advertising network, who in turn pays the publisher a share of this money. This revenue-sharing system is seen as an incentive for click fraud.
The largest of the advertising networks, Google's AdWords/AdSense and Yahoo! Search Marketing, act in a dual role, since they are also publishers themselves (on their search engines). According to critics, this complex relationship may create a conflict of interest. For instance, Google loses money to undetected click fraud when it pays out to the publisher, but it makes more money when it collects fees from the advertiser. Because of the spread between what Google collects and what Google pays out, click fraud directly and invisibly profits Google. Some have even speculated that Google's barring users of the Google Analytics system from tracing IP addresses of visitors is directly related to click fraud on the Google AdWords network and a desire to keep the true extent of click fraud from being disclosed.