Cybercriminals have been delivering malware through online display ads for years, but they appear to be making headway with a new distribution method: video advertisements.
Both methods of attack, known as malvertising, can have a broad impact and are a major headache for the ad industry. A single malicious advertisement, distributed to several highly trafficked sites, can expose tens of thousands of computers to malware in a short time.
Some ad networks and publishers have taken steps to vet their ads more thoroughly, but criminals are constantly on the lookout for weaknesses.
An attack detected about two weeks ago shows how cybercriminals are showing more interest in creating malicious video ads.
Attacks using video ads have been seen before, but this one was notable for the websites it affected, including several of the most-trafficked as ranked by Alexa.
The incident was written up earlier this month by The Media Trust, a company that's developed security tools and services for detecting malvertising.
For about 12 hours starting late on Oct. 29, some 3,000 websites served up the malicious video ad, which displayed a pop-up window nicknamed "Tripbox."
The window warned that an update was needed for browser software like Apple's Safari, and if people followed the instructions, a backdoor was downloaded to their computer.
Video ads are an attractive target for hackers because they're much harder than display ads to vet for quality, said Chris Olson, co-founder and CEO of The Media Trust.
"It's cumbersome," Olson said. "It's pieces of code running inside of a template, which is basically a container of code."
The upshot is that it's that harder to ensure that bad things aren't lurking within, and that's not lost on the bad guys, Olson said.
Video ads have been more expensive to buy than display ads, which has helped keep criminals away. They want to infect as many computers as possible, but they still have to pay for the impressions. But prices are dropping, making video a more attractive vehicle.
In the incident two weeks ago, the malicious content came from a domain called brtmedia[.]net. It was unclear if that domain is connected with BRT Media, which appears to be an online advertising company. Officials there could not immediately be reached via email.
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