Today Mobile Ad-hoc networks (MANETs) are preferred in many applications because of its self-configuring nature and dynamic topology. Sending node in MANETs rely on intermediate nodes for data transmission to remote nodes. This poses serious security threats. There is a necessity of an intrusion detection system to ensure secure message transmission in MANETs. Many Intrusion Detection Systems (IDS) like Watchdog, TWO ACKnowledgement (TWOACK), Adaptive ACKnowledgement (AACK) and Enhanced Adaptive ACKnowledgement (EAACK) have been proposed for this purpose. Of these IDS, EAACK is found to perform better. EAACK is purely acknowledgement based. Hence there should be a mechanism to validate the acknowledgements. This paper aims at improving performance of EAACK by using hybrid cryptography to validate the sending and receiving nodes in place of Digital Signature Algorithm (DSA) and Rivest Shamir and Adelman algorithm (RSA) that is used in existing EAACK. In hybrid cryptographic key exchange algorithm, a combination of symmetric and asymmetric key cryptographic algorithm (AES and RSA) is used. When compared with its contemporary EAACK, Improved EAACK (IEAACK) achieves smaller network overhead.To simulate the IEAACK environment, NS2 simulator is used. IEAACKovercomes the problems of existing IDS.