http://www.techcrunch.com/2009/01/27/repor...at-record-high/

"17.1% of all clickthroughs on web advertising are the result of click fraud - the act of clicking on a web ad to artificially increase its click-through rate - according to the latest report from Click Forensics, a company that specializes in monitoring and preventing internet crime. The level of clickfraud is the highest the company has seen since it started monitoring for it in 2006, dashing our hopes that it might hold steady in 2008. The company recorded a rate of 16.3% in Q1 2008."