A new study finds about 10% of websites that claim to comply with online advertising standards are running ads that violate those standards. The finding tells researchers that the ad-filtering rules browser extensions use to enforce the standards have flaws advertisers can take advantage of to display non-compliant ads.

Online advertising is an essential revenue generator for many websites, but these ads can also disrupt user experience: they can be annoying, slow down run times, and sometimes put privacy of users at risk by collecting user data without consent.

In response to user concerns and the increasing use of ad-blocking web browser extensions, in 2011 a group of advertisers, ad-tech providers, advertising agencies, publishers, and content creators came together to create standards for online ads that attempted to find a balance between the revenue-generating needs of web creators and the concerns raised by users.

Online ads that comply with these standards – collectively referred to as the Acceptable Ads Standard – are not blocked by most ad blockers, which use the standards to filter out unwanted ads and allow compliant ads through.

“I have some familiarity with the Acceptable Ads Standard, and I continued to see ads that seemed to violate the standard on sites that were purportedly in compliance,” says Ahsan Zafar, first author of a paper on the work and a Ph.D. student at North Carolina State University. “That led me to wonder about the extent to which websites that said they were complying with the standard were actually complying with the standard. And, if these sites are running ads that are not in compliance, what’s going on?”

For this study, the researchers focused on the 10,000 domains that have agreed to make use of the Acceptable Ads Standard and that have the highest rankings on Tranco’s “top 100K” list of the most popular websites.

The researchers created a custom webcrawler that automated the process of going through the 10,000 targeted websites to find ads that had been designated as complying with the Acceptable Ads Standard.

The researchers found that 991, or 9.91%, of the sites ran at least one ad that violated the Acceptable Ads Standard.

“We found that oversized ads and overlay ads – which covered up some of the content – were the most frequent violators of the Acceptable Ads Standard, though there were also popup ads, autoplay media and so on,” says Zafar.

“In theory, these ads should not have been viewed as compliant and should have been blocked by the ad-blocking browser extension,” says Anupam Das, senior author of the paper and an assistant professor of computer science at NC State. “The fact that these ads were not blocked tells us there are design flaws that allow ad creators to bypass size and format restrictions.

“To be clear, the ad creators may not even know they’re violating the Advertising Ad Standard. They may just make an ad and see if the browser extension allows it. However, it’s also possible they know there’s a loophole and they’re taking advantage of it.”

“After investigating how these ads could be slipping through, we found that some of the rules used by ad-blocking extensions to determine Ads Standard compliance are simply too permissive or too general – for example, not enforcing size limits on ads,” says Zafar.

To address this, the researchers made relatively modest changes to the Ads Standard compliance rules and tested these modified rules against the noncompliant ads they had already identified.

“We found that our modified rules caught substantially more violating ads, and that 32% of the 991 websites we found running noncompliant ads would actually have been in compliance,” Zafar says. “However, there was also a slight increase in the number of compliant ads that were blocked.”

“This was preliminary, proof-of-concept work,” Das says. “And we feel it is possible to develop fine-grained exception rules that could replace the overly permissive ones, reducing the number of noncompliant ads without increasing the number of compliant ads that are blocked. That work is moving forward.”

The paper, “Assessing Compliance in Digital Advertising: A Deep Dive into Acceptable Ads Standards,” will be presented May 1 at the ACM Web Conference being held in Sydney, Australia. The work was done with support from the National Science Foundation under grant number CNS-2138138.