Mobile ad hoc networks (MANETs) are collections of autonomous mobile nodes with links that are made or broken in an arbitrary way. They have no fixed infrastructure and may have constrained resources. The next generation of IT applications is expected to rely heavily on such networks. However, before they can be successfully deployed several security threats must be addressed. These are mainly due to the ad hoc nature of these networks. Consequently it may be much harder (or even impossible) to establish routing communication paths that can tolerate malicious faults. In this paper we first propose a general Bayesian model that satisfies the basic mobility requirements of a MANET and define the requirements for secure communication in this model. We then consider several multipath routing schemes and propose a new adaptive multipath routing algorithm that satisfies our security requirements.