The level of fraudulent clicks on legit online advertisements rose to 22.3% in the third quarter, ending September 30, according to summary findings released today by online ad tracking firm Click Forensics.

That's up from 14.1% during the same three months of 2009. "During the past quarter, we saw a growing volume of click fraud flow through a more diverse number of sources," says Paul Pellman, CEO of Click Forensics. "As advertising in videos, social networks and mobile devices continues to grow, advertisers will need to pay close attention to the quality of traffic they receive."

Advertisers have wasted tens of millions of dollars on faked clicks, as we reported in this story.

Most often, cybercriminals put up websites carrying online ads and no other content. The criminals then retain the services of cybergangs in control of sprawling networks of infected PCs, called botnets, which are directed to repeatedly click on the ads. This triggers payments to the crooks who put up the Web page.

Click fraud continues to steadily erode the credibility of Internet-based advertising, which is why Microsoft has declared war on cybercriminals who specialize in click fraud, as we reported here.

Context supplied earlier this year by Brad Smith, Microsoft senior vice president and general counsel, bears repeating.

Smith told reporters at a press briefing in May that criminals are "not alone" in getting rich. Smith outlined how Google, Microsoft and Yahoo, the biggest online advertising platform providers, also profit from click fraud, since each also gets a piece of the payment advertisers pay for each faked click.

The tech giants can "take aggressive steps" to stop click fraud, "or look the other way and make money on it," noted Smith. "We don't believe looking the other way is an option."

By Byron Acohido