This thesis proposes two protocols for addressing collaborative blackhole attacks in MANETs, referred to as the Detecting Blackhole Attack-Dynamic Source Routing (DBA- DSR) and Detecting Collaborative Blackhole Attack (DCBA) algorithms. The DBA-DSR protocol uses fake Route request packets to attract the malicious nodes before the actual routing process. The DCBA protocol uses our so-called suspicious value, which is based on the abnormal difference between the routing messages transmitted through a node, to identify the malicious nodes. In later stage, if the destination node detects significant loss in data packets, the initial detecting mechanism will be triggered again to identify malicious nodes. Simulation results are provided, showing significant improvement over the DSR protocol, as well as the Baited blackhole DSR protocol(chosen as a benchmark scheme), in terms of performance metrics such as packet delivery ratio, network throughput, average-end-to-end delay and routing overhead.