Security researchers have discovered malicious code in an Android application that has gathered over 100 million downloads on Google Play.
Called CamScanner, the application is a phone-based PDF creator that provides OCR (optical character recognition) capabilities. A legitimate app, CamScanner used ads for monetization and also featured in-app purchase options.
More recent versions of the application, however, were found to include an advertising library packing a malicious module, Kaspersky’s security researchers say.
Detected as Trojan-Dropper.AndroidOS.Necro.n, the malicious module was previously detected in apps preinstalled on Chinese smartphones. Functioning as a Trojan dropper, it can extract and run another malicious module from an encrypted file included in the app’s resources.
The dropped malware turns out to be a Trojan Downloader capable of fetching and loading additional malicious modules, based on creators’ intentions.
Some of the CamScanner’s users noticed the suspicious behavior and warned of that in reviews on the app’s Google Play page. Google removed the software after Kaspersky reported it.
The latest update of CamScanner, Kaspersky says, appears to have removed the malicious code, but the security researchers warn that the versions of the app may vary between different devices, meaning that some might still contain the module.
“Any app — even one from an official store, even one with a good reputation, and even one with millions of positive reviews and a big, loyal user base —can turn into malware overnight. Every app is just one update away from a major change,” Kaspersky concludes.