I. Introduction
The rapid growth of mobile devices and remarkable advances in 4G/5G mobile networking technologies have both inspired and facilitated a plethora of mobile applications (apps). In support of these mobile devices, various mobile operating systems have been developed, such as Android, iOS, and BlackBerry 10, etc. Among these mobile operating systems, Android has become the most popular one because of numerous mobile apps it provides. Unfortunately, smartphones running Android have been increasingly targeted by attackers and infected with malicious apps: according to the mobile threat report released by F-Secure in 2014 Q1 [1], over 95% of malicious apps were distributed on the Android platform. Moreover, as the major sources of Android apps, third-party markets contain a lot of cracked or tampered apps, and there is no sign to indicate whether the apps have been checked for security risks or not in these third-party markets. The lack of security inspection on Android apps intensifies the spreading of malicious apps (malware) on the Android platform. Zhou et al. [2] performed some Android malware analysis by popular security software tools, and the detection rate was only between 20.2% and 79.6%, which clearly indicates an urgent and rapidly growing demand on malware detection for Android applications.