Currently emerging standard routing protocols for MANETs do not perform well in presence of malicious nodes that intentionally drop data traffic but otherwise behave correctly with respect to control messages of the routing protocol. In this paper, we address the problem of coping with the presence of such nodes in networks that use a linkstate routing protocol. The solution, based on the verification of the principle of flow conservation, is purely protocolar and does not rely on any specific underlying OSI layer 1 or 2 technical feature. In addition, it is well suited for integration into existing link-state routing protocols for ad hoc networks, by using existing periodic control messages and by not requiring any clock synchronization between the nodes. The method, once implemented in an actual routing protocol, proves to increase the ratio of successfully delivered data packets significantly. Key words: ad hoc networks, link-state routing, security, resilience.