be downloaded, resulting in fewer constraints to AndroZoo’s users, who otherwise have to download all the available apps of AndroZoo, confronting massive resource costs (e.g., bandwidth and disk).

Table \[tab:overview\] presents an overview of the metadata we currently provide. So far, we have collected for the research community four types of metadata containing in total 24 items. We now provide brief descriptions to them respectively.

APK
---

Android apps are released and distributed through APK files. For each Android APK file, we provide six artefacts for our fellow researchers.

-   **SHA256, SHA1, MD5:** We provide three hash values (SHA256, SHA1, and MD5) to uniquely identify an Android app.

-   **APK Size:** We provide the APK size information (in byte) of a given app aiming at providing a quick means for researchers to calculate how much space they may need in order to download the app from [[**AndroZoo**]{}]{} to their local disk.

-   **Market:** For each APK, when crawling from a market, we also record from which market it is downloaded. Since we do not have a good means to check if a given APK has already been downloaded from other markets, the same APK could be downloaded from several markets. 