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 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 it significantly improves the network capabilities of wireless devices, while having a low computation and communication overhead. Moreover, we evaluate the security overhead of JANUS against two type of attacks: a less aggressive, but sufficient for some applications, model of selfish attackers, and purely malicious attacks.