Consumers and enterprise customers expect the apps they download from Google Play, Apple's App Store, and other officially sanctioned app repositories to be secure and have at least minimal respect for privacy. But security researchers at Lookout found 238 applications in Google Play that hid BeiTaAd, a well-obfuscated ad plugin that could display ads on the device's lock screen, trigger video and audio advertisements even while the phone is asleep, and display ads outside the app that interfered with the user experience in other applications.
Kristina Balaam, security intelligence engineer at Lookout and author of the blog post on the research, says that the company's research into the apps began with a phone call. "We [Lookout] got a support call from an enterprise user who noticed strange pop-up ads on their devices," Balaam says. "The support person contacted the research team, we started digging through the apps, and realized that there were other samples."
What they found was a collection of 238 apps from a single publisher, all of which contained adware that someone had gone to great lengths to hide. The publisher, CooTek, is known for legitimate Android apps and is listed on the NYSE. And the simple presence of adware in free apps isn't unprecedented: Many publishers use in-app advertising as a way to profit from free apps. The difference in this case, Balaam says, is that "as official stores start to lock down the ads that can be shown, the publishers have to become more creative in how they hide adware."
In the case of the CooTek apps, someone used very sophisticated techniques to obfuscate the adware executable bundled with the app. The adware was renamed, given a different filetype extension, and given AES encryption. All of this might have been a small annoyance, but BeiTaAd is so aggressive that it effectively rendered the device unusable for enterprise purposes.
The combination of CooTek apps and BeiTaAd adware was effective at spreading the ads to a wide audience. In a screen shot used in the research report, one of the apps — TouchPal Keyboard — shows more than 100,000,000 downloads. Together, the infected apps showed more than 440 million downloads, according to Lookout.
The research report states that as of May 23, 2019, all affected apps had been either removed from Google Play or updated to versions that do not contain BeiTaAd. Still, Balaam says, "Whoever is responsible for this plug-in, they're aware that it doesn't comply with the Google terms of service." She doesn't point a finger at the company or any individual, but continues, "Someone knew that what they were doing was wrong and they tried not to get caught."