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Jeff Horwich: We seem to have averted a prophesied mass internet outage today. According to the Wall Street Journal, Internet service providers stepped up their game over the weekend to make sure customers could get online. But the threat that created this scare -- something called "click fraud" -- is still a real danger.

Here's Marketplace's Queena Kim.

Queena Kim: This story started last November when the FBI busted a ring of cyber criminals in Estonia. Jenny Shearer is a spokeswoman for the FBI.

Jenny Shearer: We call this “Operation Ghost Click.”

This is how it worked. Cyber criminals hijacked ad space on a real website say, like, Marketplace. The ads looked real, but when victims clicked...

Shearer: Rather than the legitimate ad that was supposed to be on that webpage, there was an ad that the criminals wanted you to go to.

And the bad guys got paid for the clicks. It’s called “click fraud.” The cyber-criminals in Estonia made about $14 million from this scam.

Cameron Camp is a researcher at Eset, an antivirus software firm. He says those big dollars are spawning copycats.

Cameron Camp: Click fraud in general is sky rocketing, scammers are like any other kind of thief if a scam works once they’re going to do it again.

And so if you click on an ad for a Home Depot sale but end up at site selling fake pharmaceuticals, there’s a good chance that you’ve been a victim of click fraud.

In San Francisco, I’m Queena Kim for Marketplace.