This paper describes REWARD, a novel routing algorithm for wireless sensor networks. The algorithm is adjustable and can wage counter attacks against either single black holes or teams of malicious nodes. The proposed routing technique is suitable for network nodes that can tune their transmit power. REWARD forwards packets using geographic routing. The algorithm utilizes two types of broadcast messages, MISS and SAMBA, to organize a distributed data base for detected black hole attacks. The method has different levels of security which can be set according to the local conditions. In order to determine the effectiveness of REWARD we developed ANTS, a simulation environment which models the operation of a wireless sensor network.