DroidLegacy: Automated Familial Classification of Android Malware

We present an automated method for extracting familial signatures for Android malware, i.e., signatures that identify malware produced by piggybacking potentially different benign applications with the same (or similar) malicious code. The APK classes that constitute malware code in a repackaged application are separated from the benign code and the Android API calls used by the malicious modules are extracted to create a signature. A piggybacked malicious app can be detected by first decomposing it into loosely coupled modules and then matching the Android API calls called by each of the modules against the signatures of the known malware families. Since the signatures are based on Android API calls, they are related to the core malware behavior, and thus are more resilient to obfuscations. In triage, AV companies need to automatically classify large number of samples so as to optimize assignment of human analysts. They need a system that gives low false negatives even if it is at the cost of higher false positives. Keeping this goal in mind, we fine tuned our system and used standard 10 fold cross validation over a dataset of 1,052 malicious APKs and 48 benign APKs to verify our algorithm. Results show that we have 94% accuracy, 97% precision, and 93% recall when separating benign from malware. We successfully classified our entire malware dataset into 11 families with 98% accuracy, 87% precision, and 94% recall.