1 Million Third-Party Android Devices Have a Secret Backdoor for Scammers

Researchers from multiple firms say that the campaign seems to come from a loosely connected ecosystem of fraud groups rather than one single actor. Each group has its own versions of the Badbox 2.0 backdoor and malware modules and distributes the software in a variety of ways. In some cases, malicious apps come preinstalled on compromised devices, but in many examples that the researchers tracked, attackers are tricking users into unknowingly installing compromised apps.

The researchers highlight a technique in which the scammers create a benign app—say, a game—post it in Google’s Play Store to show that it’s been vetted, but then trick users into downloading nearly identical versions of the app that are not hosted in official app stores and are malicious. Such “evil twin” apps showed up at least 24 times, the researchers say, allowing the attackers to run ad fraud in the Google Play versions of their apps, and distribute malware in their imposter apps. Human also found that the scammers distributed over 200 compromised, re-bundled versions of popular, mainstream apps as yet another way of spreading their backdoors.

“We saw four different types of fraud modules—two ad fraud ones, one fake click one, and then the residential proxy network one—but it’s extensible,” says Lindsay Kaye, Human’s vice president of threat intelligence. “So you can imagine how, if time had gone on and they were able to develop more modules, maybe forge more relationships, there is the opportunity to have additional ones.”

Researchers from the security firm Trend Micro collaborated with Human on the Badbox 2.0 investigation, particularly focusing on the actors behind the activity.

“The scale of the operation is huge,” says Fyodor Yarochkin, a Trend Micro senior threat researcher. He added that while there are “easily up to a million devices online” for any of the groups, “This is only a number of devices that are currently connected to their platform. If you count all the devices that would probably have their payload, it probably would be exceeding a few millions.”

Yarochkin adds that many of the groups involved in the campaigns seem to have some connection to Chinese gray market advertising and marketing firms. More than a decade ago, Yarochkin explains, there were multiple legal cases in China in which companies had installed “silent” plugins on devices and used them for a diverse array of seemingly fraudulent activity.

“The companies that basically survived that age of 2015 were the companies who adapted,” Yarochkin says. He notes that his investigations have now identified multiple “business entities” in China which appear to be linked back to some of the groups involved in Badbox 2. The connections include both economic and technical links. “We identified their addresses, we’ve seen some pictures of their offices, they have accounts of some employees on LinkedIn,” he says.

Human, Trend Micro, and Google also collaborated with the internet security group Shadow Server to neuter as much Badbox 2.0 infrastructure as possible by sinkholing the botnet so it essentially sends its traffic and requests for instructions into a void. But the researchers caution that after scammers pivoted following revelations about the original Badbox scheme, it’s unlikely that exposing Badbox 2.0 will permanently end the activity.

“As a consumer, you should keep in mind that if the device is too cheap to be true, you should be prepared that there might be some additional surprises hidden in the device,” Trend Micro’s Yarochkin says. “There is no free cheese unless the cheese is in a mousetrap.”