ESET researchers have discovered a yearlong campaign on Google Play with eight million installs of adware by ESET as Android/AdDisplay.Ashas.  The team managed to track down the malware’s developer and discover additional adware-laden apps.

“We identified 42 apps on Google Play as belonging to this adware campaign, with 21 still available at the  time of discovery. The Google security team removed all of them based on our report. However, they are still available in third-party app stores,” says Lukáš Štefanko, ESET malware researcher.

The apps provide the functionality they promise - including video downloading, simple gaming and radio play - besides working as adware. “The adware functionality is the same in all apps we analysed,” says Štefanko.

The apps use several tricks to reach users’ devices and remain undetected: checking for Google Play’s security testing mechanism; delaying the display of ads until well after the device is unlocked; hiding their icons and creating shortcuts instead.

The ads delivered by the adware are displayed as full-screen activity. If the user wants to check which app is responsible for the ad being displayed, the app impersonates Facebook or Google. “The adware mimics these two apps to look legitimate and avoid suspicion - and thus stay on the affected device for as long as possible,” says Štefanko.

Another point of interest is that the Ashas adware family has hidden its code under the com.google.xxx package name. “Posing as part of a legitimate Google service may help avoid scrutiny. Some detection mechanisms and sandboxes may whitelist such package names in an effort to prevent wasting resources,” elaborates Štefanko.

Whilst analysing the apps, ESET researchers noticed that the malicious developer left many traces behind.  Using open-source information, they tracked down the developer of the adware, whom they also identified as the campaign’s operator and owner of the C&C server. Štefanko notes that “establishing the developer’s identity was a side effect of our hunt for further malware and campaigns.”

While adware might not be as damaging as some other forms of malware, the fact that it can sneak into the official Android app store so easily is disturbing.  “Users should protect their devices by sticking with basic cybersecurity principles and using a quality security solution,” recommends ESET’s Štefanko.