Secure routing is vital to the acceptance and use of Wireless Sensor Networks (WSN) for many applications. However, providing secure routing in WSNs is a challenging task due to the inherently constrained capabilities of sensor nodes. Although a wide variety of routing protocols have been proposed for WSNs, most do not take security into account as a main goal. Routing attacks can have devastating effects on WSNs and present a major challenge when designing robust security mechanisms for WSNs. In this paper, we examine some of the most common routing attacks in WSNs. In particular, we focus on the wormhole routing attack in some detail. A variety of countermeasures have been proposed in the literature for such attacks. However, most of these countermeasures suffer from flaws that essentially render them ineffective for use in large scale WSN deployments. Due to the inherent constraints found in WSNs, there is a need for lightweight and robust security mechanisms. The examination of the...