Peer-to-peer applications are emerging into mobile devices. However, resource limitations of these devices introduce new challenges for P2P technologies. For instance, there is a need for incentive mechanisms, which address the free riding problem but do not waste devices’ battery or communication resources. A centralized and user-identity based incentive mechanism enables mobile users to contribute with any device and receive P2P services with mobile devices. We explore security issues related to a centralized incentive mechanism by analyzing and classifying threats and potential security mechanisms. We propose a privacy preserving security architecture. The architecture is based on authentication, software tamper protection, and misbehavior detection mechanisms. Further, we provide a discussion on potential security compromises, not jeopardizing sufficient security level, and describe a prototype implementation for mobile BitTorrent file sharing peers.