This document discusses intrusion detection systems (IDS) and different techniques used for IDS, including clustering-based detection. It first provides background on IDS, describing their purpose of detecting intruders and protecting systems. It then outlines various IDS types, including mobile agent-based, cluster-based, cryptography-based, and others. The document also summarizes related work from other papers applying data mining techniques like clustering to improve IDS detection rates and reduce false alarms. Finally, it discusses problems with current and traditional IDS, such as threshold detection leading to false positives, and false negatives where attacks are missed.