"Bot fraudsters" account for almost 25% of the views from watching online video advertisements, a new investigation into the digital advertising industry has revealed.
The report for the Association of National Advertisers (ANA), conducted by web security company White Ops, showed that large companies such as Ford, Intel and Mastercard have been scammed by online fraudsters.
The malicious software, hacked into the computers of millions globally by the fraudsters, is set to cost advertisers $6.3bn (£4.02bn) in 2015.
"The bot traffic looks like legitimate human traffic," said one of the founders of White Op, Michael Tiffany. "You can make your bogus website look popular and pocket a bunch of money."
The software infects computers with malware which copies the behaviour of a human viewer, watching certain videos, clicking on website ads and placing things in shopping carts.
"The survey confirms a deep, dark fear that people know is out there," Bill Duggan, group executive vice-president of the ANA, told The Guardian.
"Digital is supposed to be this great new accountable thing, but if we know it's not reaching the right people that money is wasted."
According to the Anti-Phishing Working Group, nearly a third of all the world's computers have become infected with the software from organised criminals.