A US company that specialises in detecting online advertising fraud says a Russian crime group has been siphoning off millions of dollars in advertising revenue each day for a couple of months.
The New York-based company White Ops says the scam may have so far cost brands, and potentially media companies, hundreds of millions of dollars.
It released a report on Wednesday saying the "Methbot" scam made it look as though hundreds of thousands of people, mostly in the US, had watched video advertisements from real companies on more than 6,000 fake websites that mimicked well-known publishers, including CNN, ESPN, Vogue and The New York Times, when nobody was actually watching.
The criminal ring's gains have come directly out of the pockets of companies paying for digital ads and also, potentially, of the websites that could have hosted those ads.
White Ops president Eddie Schwartz said he can't put a total value on the amount the Russian group has stolen, because it's not clear when the scam began. But he estimates the scammers have been getting between $US3 million ($A4.1 million) and $US5 million ($A6.9 million) each day since roughly early October and the scam is ongoing.
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The revelations are likely to make it harder for legitimate online publishers to make profit from advertising if brands become more suspicious, said Forrester digital publishing expert Susan Bidel.
"It's the advertiser's money that's being stolen, it's the publisher's reputation. It punishes all of publishing," she said.
Bidel said brands need to insist that advertising-technology platforms and ad agencies show them exactly what they are paying for and where ads end up.
Fraud has long been a problem in the roughly $US187 billion global digital-ad market.
