http://www.computerworld.com/action/article.do?command=viewArticleBasic&taxonomyName=internet_business&articleId=9131999&taxonomyId=71&intsrc=kc_top

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Click Forensics generates its quarterly click-fraud incidence report using its Click Fraud Index, which gathers data from more than 4,500 online advertisers and agencies that use ad services from all major search engines.
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