Fourth-quarter click-fraud data from Click Forensics showed that click fraud increased to the highest levels for the year, reaching 14.2 percent (industry average), compared with 13.8 percent for Q3, 14.1 percent for Q2 and 13.7 percent for Q1 (via Search Engine Land).

According to the Click Fraud Index, the average click fraud rate of pay-per-click advertisements appearing on search engine content networks was 19.2 percent in Q4.

"The most interesting data points from last quarter's data was that the industry average click fraud rate climbed to its highest level in 2006 and that the click fraud rate for affiliate sites was significantly higher than the overall industry average," said Tom Cuthbert, president and CEO of Click Forensics.

The industry average click fraud rate for high-priced search terms - those that cost over $2.00 - remained at 20.9 percent, unchanged from Q3 and from 20.2 percent in Q2. High-priced terms often make up the majority of an advertiser's total spend.

The average PPC term cost for the top key terms across the five biggest search advertising industries - Retail, Financial Services, Health & Fitness, Technology, and Entertainment - was $3.50 in Q4, compared with $3.92 in Q3, $4.51 in Q2 and $4.75 in Q1.