Abstract— Discovery of Ranking Fraud for Mobile Apps. Ranking fraud in the mobile App market refers to fraudulent or deceptive activities which have a purpose of bumping up the Apps in the popularity list. Indeed, it becomes more and more frequent for App developers to use shady means, such as inﬂating their Apps’ sales or posting phony < Final Year Projects 2016 > App ratings, to commit ranking fraud. While the importance of preventing ranking fraud has been widely recognized, there is limited understanding and research in this area. To this end, in this paper, we provide a holistic view of ranking fraud and propose a ranking fraud detection system for mobile Apps. Speciﬁcally, we ﬁrst propose to accurately locate the ranking fraud by mining the active periods, namely leading sessions, of mobile Apps.