Abstract. Attack analysis is a challenging problem, especially in emerging environments where there are few known attack cases. One such new environment is the Mobile Ad hoc Network (MANET). In this paper, we present a systematic approach to analyze attacks. We introduce the concept of basic events. An attack can be decomposed into certain combinations of basic events. We then define a taxonomy of anomalous basic events by analyzing the basic security goals. Attack analysis provides a basis for designing detection models. We use both specification-based and statistical-based approaches. First, normal basic events of the protocol can be modeled by an extended finite state automaton (EFSA) according to the protocol specifications. The EFSA can detect anomalous basic events that are direct violations of the specifications. Statistical learning algorithms, with statistical features, i.e., statistics on the states and transitions of the EFSA, can train an effective detection model to d...