In mobile ad-hoc networks, nodes do not rely on any routing infrastructure but relay packets for each other. Thus communication in mobile ad-hoc networks functions properly only if the participating nodes cooperate in routing and forwarding. However, it may be advantageous for individual nodes not to cooperate, for example to save power or to launch security attacks such as denial-of-service. In this paper, we give an overview of potential vulnerabilities and requirements of mobile ad-hoc networks, and of proposed prevention, detection and reaction mechanisms to thwart attacks.