The document proposes a system to detect ranking fraud in mobile applications. It identifies three types of evidence - ranking based, rating based, and review based - that can be used to detect fraudulent behavior. The proposed system first identifies leading sessions of apps based on historical ranking records. It then analyzes apps' ranking, rating, and review patterns within leading sessions to find anomalies compared to normal apps. This evidence is aggregated to reliably identify fraudulent apps in the mobile market. The system aims to enhance user experience by potentially incorporating the fraud detection into a recommender system.