Tens of adware-carrying Android applications gathered 8 million installs on Google Play before being taken down, ESET reports.
The campaign, which started in July 2018, involved a total of 42 applications hosted on Google Play, 21 of which were still available in the storefront at the time of discovery. All of the offending apps have already been removed from the application marketplace.
The adware, called Android/AdDisplay.Ashas, features the same functionality in all the analyzed apps.
When launched, the applications begin communication with the command and control (C&C) server, sending back information such as device type, OS version, language, installed apps, free storage space, battery status, root and developer mode status, and whether Facebook and Facebook Messenger are installed.
The server sends configuration data needed for displaying ads and for stealth and resilience, ESET explains.
The adware payload is not triggered if the IP address of the affected device is known to be that of a Google server. Moreover, the app can set a delay for displaying the first ad to ensure that it can avoid its behavior being detected during a typical testing procedure, which takes less than 10 minutes.
The app can also hide its icon and create a shortcut instead, so that only the shortcut is removed if the user attempts to uninstall it. The app would then continue to run in the background.
After the configuration data is received, the attackers can control the device’s display of ads. Each ad is shown in full screen and if the user attempts to check which app is responsible via the “Recent apps” button, the app displays a Facebook or Google icon to avoid suspicion.
The adware also hides its code under the com.google.xxx package name, yet another trick to avoid scrutiny, given that some detection mechanisms may whitelist packages that appear to be part of a legitimate Google service.
After discovering the adware-laden apps, ESET decided to find the campaign’s operator and owner of the C&C server. The investigation led to a list of students attending a class at a Vietnamese university, and then to the discovery of the operator’s phone number and his university ID.
The researchers also found the culprit’s email address and his GitHub repository, which proves he is an Android developer. Moreover, they discovered he also has apps in Apple’s App Store, some being iOS versions of the ones removed from Google Play, yet lacking adware functionality.
After discovering the developer’s YouTube channel, which promoted the Ashas adware, and his Facebook profile, the researchers discovered that he was promoting a slew of games, some that didn’t contain any adware functionality. ESET also discovered additional apps that contained adware functionality and were available on Google Play.
“Seeing that the developer did not take any measures to protect his identity, it seems likely that his intentions weren’t dishonest at first – and this is also supported by the fact that not all his published apps contained unwanted ads,” ESET notes.
The researchers also pointed out that the developer was aware of the malicious nature of the added adware functionality, given the various stealth and resilience techniques he implemented.