This paper brings forth a distributed self adaptive intrusion detection system (IDS) based on programmable mobile agents which can act as a key line of defense against major security attacks. The proposed intrusion detection model is organized as a combination of the two trends in IDS; the rule based and the behavior based scheme. Also this model draws out the merits of both the host based and networks based IDSs and deploy them wisely considering the critical features of MANETs. In contrast to many proposed and implemented IDSs, this is an efficient framework conscious of the inherent constraints of MANETS and are self adaptive in nature. In addition to this, the use of light weight mobile agents provide a low overhead mechanism which in turn is well suited to MANET characteristics. Through this paper, an attempt to improvise the mobile agents is done by making it tamper evident which is very essential as the agents can be compromised and thereby turning all the efforts of the IDS futile.