The security concerns for a Peer-to-Peer implementation of Nomadic Networks are described with special emphasis on taxonomy and on their identification. The underpinning reference question is how to provide a wide scope of secure networking functions in a completely decentralized and unmanaged network (an ad hoc mobile nomadic network). Though many of the identified security concerns apply to any overlay network, the complete selection of concerns is based on their possible importance in an implementation such as the AmIGo Project collaboration for a ubiquitous nomadic network. APPEARS IN: Peer-to-Peer Computing: The Evolution of Disruptive Technology, edited by Goodman and Subramanian, Idea Group Inc., 2003