The click fraud rate for online ads is increasing this year, according to a new report from Click Forensics. The click fraud rate in the second quarter this year was 15.8 percent, with a 14.1 percent rise over the same period last year and 14.8 percent increase from the first quarter this year.

Click Forensics also indicated the fraud rate within large pay-per-click networks is more serious – making up 25.6 percent of all fraudulent traffic in the second quarter, increasing 21.9 percent over the same period 2006 and 19.2 percent over the preceding quarter.

Yahoo! shielded itself from the report, claiming that its advertisers have not been charged for 12 to 15 percent of clicks because of the fraud.

Google, on the other hand, questioned the research's findings and accused Click Forensics of inflating the figures in order to attract more business from advertisers. Google also said the fraud clicks have already been identified, and were never billed to advertisers.