Opportunistic Network (OppNet) is a subclass of the DelayDisruption Tolerant Network (DTN). There is no end-to-end connection between Opportunistic Mobile Nodes (OMNs). So, there are lots of opportunity for invader into the network. That's why, security and privacy of opportunistic network is one of the important aspect of research. OppNet security is designed to serve as a Handbook for UG, PG students, Teachers, Researchers and Engineers in the disciplines of Information Technology, Computer Science and Engineering, Electronics and Communication Engineering. It explains the fundamental of Opportunistic Networks and its security and also provides practical information about the various aspects of the OppNet security that are currently in use.