A number of factors, such as the increasing popularity of wireless networks, the opportunities offered by 3G services, and the rapid proliferation of mobile devices, have stimulated a general trend towards extending Peer-to-Peer (P2P) characteristics to wireless environments. As a result, the P2P paradigm has begun to migrate to pervasive computing scenarios. So far, research in this domain has led to some middleware models working over Mobile Ad Hoc Networks (MANETs), which are now viewed as a Mobile-P2P (M-P2P) networks. However, the highly dynamic, decentralized and self-organizing nature of MANETs does not fit well with many approaches developed in the P2P world. In particular, it does not seem easy to deploy security solutions for M-P2P due, among other reasons, to the inherent limitations of the peers? devices and their potentially very sporadic interaction with other peers. Under these assumptions, a significant challenge is how to establish a decentralized trust management system. In this paper, we first summarize the advances in M-P2P security services and point out potential future applications based on opportunistic interactions. Then, we discuss several kind of threats and attacks, and finally analyze the (un)suitability of employing trust-based systems in some of these environments.