Opportunistic data forwarding has drawn much attention in the research community of multihop wireless networking, with most research conducted for stationary wireless networks. One of the reasons why opportunistic data forwarding has not been widely utilized in mobile ad hoc networks (MANETs) is the lack of an efficient lightweight secure routing scheme with strong source routing capability. In this paper, a lightweight secure source routing (SSR) protocol is proposed which is used to bypass insecure nodes and make sure transmission takes place only through secure nodes to the destination. SSR can maintain more network topology information than distance vector (DV) routing to facilitate source routing, although it has much smaller overhead than traditional DV-based protocols [e.g., destination-sequenced DV (DSDV)], link state (LS)-based routing [e.g., optimized link state routing (OLSR)], and reactive source routing [e.g., dynamic source routing (DSR)]. Computer simulation in Network Simulator 2 (ns-2) ensure security of transmission with less overhead in PSR protocols.