Mobile Ad-hoc Networks (MANETs) are widely used nowadays. Because of their characteristics as open media, dynamic topology, being infrastructure-less and lack of centralized monitoring, MANET is vulnerable to a wide range of attacks like blackhole and grayhole. Blackhole and grayhole attacks refer to the attacks that breach the security by performing packet forwarding and routing misbehavior and cause denial of service in MANETs. In this paper we improved our previous work on MCBDS, we reduced false-positive rate more than before and on average it dropped to zero. The proposed method employs Network Simulator-2 (NS-2) to validate the effectiveness under different scenarios. Simulation results show that improved MCBDS has same performance as CBDS in terms of throughput and end-to-end delay and as much as the presence of malicious nodes increased, improved MCBDS performs better than CBDS.