Attacks on network infrastructure presently are main threats against network and information security. With rapidly growing unauthorized activities in network, Intrusion Detection (ID) as a component of defense-in-depth is very necessary because traditional firewall techniques cannot provide complete protection against intrusion. ID is an active and important research area of network security. A survey on ID technology is shown in this paper. It is involved with several main aspects of ID technology. Analyses on intrusion detection techniques and data collection techniques are emphasized. Some novel developments in ID Systems, such as both data mining based ID Systems and data fusion based ID Systems, also are discussed. Current ID technology faces some powerful cjallenges, some main challenges and future promising directions are presented.