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Hybrid networks consisting of cellular and Wi-Fi networks were proposed as a high-throughput architecture for cellular services. In such networks, devices equipped with cellular and Wi-Fi network cards access Internet services through the cellular base station. The Wi-Fi interface is used to provide a better service to clients that are far away from the base station, via multihop ad hoc paths. The modified trust model of hybrid networks generates a set of new security challenges as clients rely on intermediate nodes to participate effectively in the resource reservation process and data forwarding. In this paper, we introduce JANUS, a framework for scalable, secure, and efficient routing for hybrid cellular and Wi-Fi networks. JANUS uses a scalable routing algorithm with multiple channel access, for improved network throughput. In addition, it provides protection against selfish nodes through a secure crediting protocol and protection against malicious nodes through secure route establishment and data forwarding mechanisms. We evaluate JANUS experimentally and show that its performance is 85 percent of the optimum algorithm, improving with a factor greater than 50 percent over previous work. We evaluate the security overhead of JANUS against two types of attacks: less aggressive, but sufficient for some applications, selfish attacks and purely malicious attacks.