Mobile ad-hoc network is an interesting network, which is classified as an autonomous system. These types of networks are constructed based on low capacity wireless links, without having a centralized infrastructure system. Lack of central monitoring system makes it so vulnerable to an insider attack. These attacks consist of two main categories; false data and false route attack. An efficient intrusion detection system (IDS) should have a good understanding about the categories. It can be defined by comparison between (true positive network throughput/false throughput) and the packet delivery ratio. This paper, DNACK is proposed based on Digital Signature and standard method of Negative Acknowledgment, which is a new method of false data detection in case of en-route filtering IDS. DNACK members can detect both kinds of insider attacks, a false data (false data injected and false modified messages) and false route attacks (packet dropping and flooding attack), regards to DNACK characteristic. The false data will be detected based on source digital signature by upcoming member and the routing attacks, will be monitored by the last member. The network efficiency shall be guaranteed by using of DNACK because of the high percentage of Packet delivery and the minimum of false throughput.