Opportunistic Network (OppNet) is a subclass of the Delay\Disruption Tolerant Network (DTN). There is no end-to-end connection between Opportunistic Mobile Nodes (OMNs). So, there are lots of opportunities for invaders into the network. That is why the security and privacy of opportunistic networks are important aspects 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 fundamentals of Opportunistic Networks and their security and provides practical information about the various aspects of OppNet security currently in use.