Title: ModZoo: A Large-Scale Study of Modded Android Apps and their Markets

Abstract: We present the results of the first large-scale study into Android markets that offer modified or modded apps: apps whose features and functionality have been altered by a third-party. We analyse over 146k (thousand) apps obtained from 13 of the most popular modded app markets. Around 90% of apps we collect are altered in some way when compared to the official counterparts on Google Play. Modifications include games cheats, such as infinite coins or lives; mainstream apps with premium features provided for free; and apps with modified advertising identifiers or excluded ads. We find the original app developers lose significant potential revenue due to: the provision of paid for apps for free (around 5% of the apps across all markets); the free availability of premium features that require payment in the official app; and modified advertising identifiers. While some modded apps have all trackers and ads removed (3%), in general, the installation of these apps is significantly more risky for the user than the official version: modded apps are ten times more likely to be marked as malicious and often request additional permissions.