  Download fraud is a prevalent threat in mobile App markets, where fraudsters
manipulate the number of downloads of Apps via various cheating approaches.
Purchased fake downloads can mislead recommendation and search algorithms and
further lead to bad user experience in App markets. In this paper, we
investigate download fraud problem based on a company's App Market, which is
one of the most popular Android App markets. We release a honeypot App on the
App Market and purchase fake downloads from fraudster agents to track fraud
activities in the wild. Based on our interaction with the fraudsters, we
categorize download fraud activities into three types according to their
intentions: boosting front end downloads, optimizing App search ranking, and
enhancing user acquisition&retention rate. For the download fraud aimed at
optimizing App search ranking, we select, evaluate, and validate several
features in identifying fake downloads based on billions of download data. To
get a comprehensive understanding of download fraud, we further gather stances
of App marketers, fraudster agencies, and market operators on download fraud.
The followed analysis and suggestions shed light on the ways to mitigate
download fraud in App markets and other social platforms. To the best of our
knowledge, this is the first work that investigates the download fraud problem
in mobile App markets.
