  Distributed intrustion detection systems detect attacks on computer systems
by analyzing data aggregated from distributed sources. The distributed nature
of the data sources allows patterns in the data to be seen that might not be
detectable if each of the sources were examined individually. This paper
describes the various approaches that have been developed to share and analyze
data in such systems, and discusses some issues that must be addressed before
fully decentralized distributed intrusion detection systems can be made viable.
