One of the knocks against pay-per-click advertising is concern about fraudulent clicks being made on online ads that cost advertisers money and drain their account budgets needlessly. And while Google, Yahoo and various online publishers have long held that their SEM operations can detect patterns of fraud and then credit-adjust advertisers’ accounts accordingly, that hasn’t mollified the skeptics at all.

And now SEM critics have new ammunition in the form of two click fraud reports issued in July by Anchor Intelligence and Click Forensics, two of the industry’s leading traffic auditing and traffic quality management firms. Researchers at both companies have discovered that “scripted” programs that click on ads increased in volume during the second quarter of 2009.

Click Forensics estimates that the overall average click fraud rate was nearly 13% over the quarterly period. According to the firm, this also included an ominous rise in “collusion fraud” on advertising networks. That’s when publishers rotate IP addresses (botnets) to click on ads on their own sites to generate inflated commissions from unprotected ad networks. Many ad networks have difficulty differentiating these attacks from valid clicks.

Based on these results, Click Forensics estimates that the amount of money lost yearly due to click fraud exceeds $4 billion. And while a large chunk of those dollars are presumably reimbursed to advertisers in the form of discounts or rebates, it is impossible to know what portion that amount actually represents because SEM program providers don’t share that information with the outside world.

Anchor Intelligence reported even higher rates of attempted click fraud during the second quarter 2009: nearly 23%.

Where are the nefarious attacks coming from? Richard Sim, Anchor Intelligence’s vice president of product marketing, says, “Vietnam stands out in terms of the fraud as a percentage of all traffic. Nearly one out of every two clicks from Vietnam was registered as click fraud.” That’s nearly double the rate of attempted click fraud found by Anchor Intelligence for the next highest ranked countries – Canada at ~28% and the U.S. at ~26%.

What this says is that click fraud is very much with us, despite all of the best efforts that go into trying to root it out. This should be taken into consideration by advertisers when planning and executing an online advertising program. And it wouldn’t be a bad idea to factor in a 15% or 20% “degradation” factor on all advertising goals and results when evaluating clickthrough rates and calculating ROI.

The good news is that, even with this reduction factor applied, when you compare search engine advertising against alternative forms of promotion, it’s still one of the better buys in the business.