  Since it is impossible to predict and identify all the vulnerabilities of a
network, and penetration into a system by malicious intruders cannot always be
prevented, intrusion detection systems (IDSs) are essential entities for
ensuring the security of a networked system. To be effective in carrying out
their functions, the IDSs need to be accurate, adaptive, and extensible. Given
these stringent requirements and the high level of vulnerabilities of the
current days' networks, the design of an IDS has become a very challenging
task. Although, an extensive research has been done on intrusion detection in a
distributed environment, distributed IDSs suffer from a number of drawbacks
e.g., high rates of false positives, low detection efficiency etc. In this
paper, the design of a distributed IDS is proposed that consists of a group of
autonomous and cooperating agents. In addition to its ability to detect
attacks, the system is capable of identifying and isolating compromised nodes
in the network thereby introducing fault-tolerance in its operations. The
experiments conducted on the system have shown that it has high detection
efficiency and low false positives compared to some of the currently existing
systems.
