involves making numerous searches for a keyword without clicking of the ad. Such ads are disabled automatically, enabling a competitor's lower-bid ad for the same keyword to continue, while several high bidders (on the first page of the search results) have been eliminated. Hit inflation attack A hit inflation attack is a kind of fraudulent method used by some advertisement publishers to earn unjustified revenue on the traffic they drive to the advertisers’ Web sites. It is more sophisticated and harder to detect than a simple inflation attack. This process involves the collaboration of two counterparts, a dishonest publisher, P, and a dishonest Web site, S. Web pages on S contain a script that redirects the customer to P's Web site, and this process is hidden from the customer. So, when user U retrieves a page on S, it would simulate a click or request to a page on P's site. P's site has two kinds of webpages: a manipulated version, and an original version. The manipulated version simulates a click or request to the advertisement, causing P to be credited for the click-through. P selectively determines whether to load the manipulated (and thus fraudulent) script to U's browser by checking if it was from S. This can be done through the Referrer field, which specifies the site from which the link to P was obtained. All requests from S will be loaded with the manipulated script, and thus the automatic and hidden request will be sent. This attack will silently convert every innocent visit to S to a click on the advertisement on P's page. Even worse, P can be in collaboration with several dishonest Web sites, each of which can be in collaboration with several dishonest publishers. If the advertisement commissioner visits the Web site of P, the non-fraudulent page will be displayed, and thus P cannot be accused of being fraudulent. Without a reason for suspecting that such collaboration exists, the advertisement commissioner has to inspect all the Internet sites to detect such attacks, which is infeasible. Another proposed method for detection of this type of fraud is through use of association rules. Manipulation of organic search results One major factor that affects the ranking of websites in organic search results is the CTR (Click-through Rate). That is the ratio of clicks to impressions, or in other words how many times a search result is clicked on,