Delay tolerant networks (DTNs) are a special type of intermittently connected networks (ICN) featured by variable delay, frequent disruption, asymmetric data rates, and high-error rates. The DTNs have been primarily developed for interplanetary networks (IPNs), however, it shows applicability to challenged networks. Thus, solutions devised for security and routing for traditional networks do not apply to DTNs due to its unique nature. Moreover, this paper shows less attention particularly in security and its related strings. In DTNs, malicious nodes launch various attacks that include packet drop, a fake packet, and flood attack. These attacks inevitably overuse scarce resources (bandwidth, buffer, and energy) in DTNs, which leads to low packet delivery ratio and high packet loss ratio. Flood attack is listed in top among the challenging attacks in DTNs. The existing techniques to confront flood attack suffered from high-detection time and low-detection accuracy. This paper proposed novel resources efficient (distributed and intrusion detection system-based) algorithms to mitigate flood attack. The simulation results show considerable improvement in detection time, detection accuracy, and resource consumption, and also show enhanced packet delivery ratio and reduced packet loss ratio.