An ad network provider is performing in-browser Coinhive cryptojacking on websites that use its service, 360 Netlab security researchers warn.
The practice has been ongoing since December 2017, several months after the ad network provider, a company called PopAds Publisher, started using domain generation algorithm (DGA) technology to bypass ad blockers, claiming it would allow customers to “monetize traffic that wasn’t monetized before.”
In mid-2017, the provider started to generate seemingly random domains that would ensure ads can reach end users. By the end of the year, however, these domains, which 360 Netlab refers to as DGA.popad, started participating in cryptojacking activities, all without end-users’ acknowledgement.
Given that many people use ad blockers to prevent sites from displaying ads to them, ad networks often attempt to bypass blockers, and this provider decided to use DGA domains to host its advertisements. With these domains changing daily, it becomes difficult to block the ads, the researchers point out.
What’s more, the ad network provider recently started using the DGA.popad domains to perform cryptojacking. These domains, the researchers discovered, have a strong connection with Coinhive family domains in DNS traffic and serve the coinhive.min.js web miner.
Some of the DGA.popad domains have a high ranking, with one of them found in the top 2000 sites on Alexa and several others in the top 3000 list.
Once a user accesses such a site, their computer’s CPU starts being used to the full. According to 360 Netlab, the favicon.ico on the DGA.popad sites was found to run as a web miner. Most of the sites that would redirect users to DGA.popad domains are providing adult content and downloading services.
Because the impacted sites contain advertisements from this ad network, the cryptojacking activities are performed regardless of whether the user has an ad blocker installed or not.
Normally, users would be sent to a standard domain (serve.popads.net) hosted by the provider. If an ad blocker is used, the standard domain is blocked, and the visitor is sent to one of the DGA.popad domains. Regardless of the delivery mechanism, both the ad and the cryptojacking script are served.
“We are not able to make a detailed assessment. This is because only part of all the traffic passing DGA.popad and serve.popads.net will be inserted a web miner, but we are not sure which part will be selected, for now,” the researchers note.