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Five years ago, researchers made a grim discovery—a legitimate Android app in the Google Play market that was surreptitiously made malicious by a library the developers used to earn advertising revenue. With that, the app was infected with code that caused 100 million infected devices to connect to attacker-controlled servers and download secret payloads.

Now, history is repeating itself. Researchers from the same Moscow, Russia-based security firm reported Monday that they found two new apps, downloaded from Play 11 million times, that were infected with the same malware family. The researchers, from Kaspersky, believe a malicious software developer kit for integrating advertising capabilities is once again responsible.

Clever tradecraft

Software developer kits, better known as SDKs, are apps that provide developers with frameworks that can greatly speed up the app-creation process by streamlining repetitive tasks. An unverified SDK module incorporated into the apps ostensibly supported the display of ads. Behind the scenes, it provided a host of advanced methods for stealthy communication with malicious servers, where the apps would upload user data and download malicious code that could be executed and updated at any time.