Avast Blog_ViewPoints: The enduring scourge of malvertising rears up anew

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Threat actors are gaming the online advertising ecosystem to silently spread malware like never before; why it’s up to you to protect yourself.

Malvertising is rearing its ugly head – yet again.

Malicious online ads have surged and retreated in cycles since the earliest days of the Internet. Remember when infectious banner ads and viral toolbars cluttered early browsers?

Historically, with each iteration of malicious ads, the online advertising industry, led by Google, has fought back, and kept this scourge at a publicly acceptable level.

However, malvertising has never been as dynamic, stealthy and persistent as it is today. Here’s what you should know about this enduring online threat:

Gaming the ecosystem

Malvertising has become enmeshed in the highly dynamic online advertising, shopping and banking ecosystem we’ve come to rely on. It has accomplished this by leveraging the openness of the browsers on our go-to computing devices, namely our smartphones and PCs.

Malvertising code often circulates in tiny iframes, the HTML element that enables objects to appear on a webpage without changing the page. This bad code comes and goes, circulating to even well-known, high-traffic websites as part of the flow of web ads being placed dynamically by the online advertising networks, of which Google is the largest.

Malvertisers game this ecosystem in several ways. There are endless ways for them to hack into websites and ad networks directly. Doors and windows are left wide open in the software applications being rapidly developed to support a swelling army of third-party contractors who supply shopping cart services, data management platforms, retargeting enablement systems, and the like.

“The bad guys are insinuating their malicious code as part of the code that renders on the victim’s device during fulfillment,” says Chris Olson, CEO of the Media Trust, a McLean, VA-based website security vendor. “If you visit a large retail website, you may encounter 100 or 150 third party companies that get access to your computing device. For the most part, no one is really thinking about the security of all of these third-party apps. It’s only lightly monitored.”

Another gambit favored by threat actors is to set up shop as an independent ad network, and then patiently behave as a model citizen in order to gain trust. Once good-standing is achieved, the attacker begins to slip malicious ads into the daily flow of the ecosystem. 

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