Detecting repackaged smartphone applications in third-party android marketplaces

Recent years have witnessed incredible popularity and adoption of smartphones and mobile devices, which is accompanied by large amount and wide variety of feature-rich smartphone applications. These smartphone applications (or apps), typically organized in different application marketplaces, can be conveniently browsed by mobile users and then simply clicked to install on a variety of mobile devices. In practice, besides the official marketplaces from platform vendors (e.g., Google and Apple), a number of third-party alternative marketplaces have also been created to host thousands of apps (e.g., to meet regional or localization needs). To maintain and foster a hygienic smartphone app ecosystem, there is a need for each third-party marketplace to offer quality apps to mobile users. In this paper, we perform a systematic study on six popular Android-based third-party marketplaces. Among them, we find a common "in-the-wild" practice of repackaging legitimate apps (from the official Android Market) and distributing repackaged ones via third-party marketplaces. To better understand the extent of such practice, we implement an app similarity measurement system called DroidMOSS that applies a fuzzy hashing technique to effectively localize and detect the changes from app-repackaging behavior. The experiments with DroidMOSS show a worrisome fact that 5% to 13% of apps hosted on these studied marketplaces are repackaged. Further manual investigation indicates that these repackaged apps are mainly used to replace existing in-app advertisements or embed new ones to "steal" or re-route ad revenues. We also identify a few cases with planted backdoors or malicious payloads among repackaged apps. The results call for the need of a rigorous vetting process for better regulation of third-party smartphone application marketplaces.