a family is three and 760 collected families have over 100 variants. Through a preliminary study on the collected app families, we have identified several reuse cases adopted by Android app variants, including library reuse, automated app generation, content-driven variants and device-driven variants [@li2016mining]. With an advanced study, we believe that more reuse cases, including semantic reuses, can be identified on top of our collect app family variants.

**Pairwise Similarity Analysis.** We present a research framework called SimiDroid [@li2017simidroid] that supports multi-level pairwise similarity comparison of Android apps, aiming at supporting the understanding of similarities or changes among app versions and among repackaged apps. SimiDroid is designed as a plugin-based framework that has already integrated various comparison methods such as code-based or resource-based comparisons. In addition to detect similar Android apps, we also perform a number of case studies on AndroZoo apps to demonstrate the suitability of SimiDroid in providing explanation hints for different usage scenarios. For example, we have leveraged SimiDroid to check and validate the hypothesis of multi-generation repackaging, where an original app identified in a repackaging pair is actually a repackaged app from a prior repackaging generation [@li2017the].

**Piggybacking Behaviour Understanding.** Fig. \[fig:piggybacking\] presents some basic terms 