Anomaly-based intrusion detection system

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An Anomaly-Based Intrusion Detection System, is a system for detecting computer intrusions and misuse by monitoring system activity and classifying it as either normal or anomalous. The classification is based on heuristics or rules, rather than patterns or signatures, and attempts to detect any type of misuse that falls out of normal system operation. This is as opposed to signature-based systems, which can only detect attacks for which a signature has previously been created.[1]

In order to determine what is attack traffic, the system must be taught to recognize normal system activity. This can be accomplished in several ways, most often with artificial intelligence type techniques. Systems using neural networks have been used to great effect. Another method is to define what normal usage of the system comprises using a strict mathematical model, and flag any deviation from this as an attack. This is known as strict anomaly detection.[2]

Anomaly-based Intrusion Detection does have some shortcomings, namely a high false-positive rate and the ability to be fooled by a correctly delivered attack.[2] Attempts have been made to address these issues through techniques used by PAYL[1] and MCPAD.[3]

See also[edit]


  1. ^ a b Wang, Ke. "Anomalous Payload-Based Network Intrusion Detection" (PDF). Recent Advances in Intrusion Detection. Springer Berlin. doi:10.1007/978-3-540-30143-1_11. Retrieved 2011-04-22. 
  2. ^ a b A strict anomaly detection model for IDS, Phrack 56 0x11, Sasha/Beetle
  3. ^ Perdisci, Roberto; Davide Ariu; Prahlad Fogla; Giorgio Giacinto; Wenke Lee (2009). "McPAD : A Multiple Classifier System for Accurate Payload-based Anomaly Detection" (PDF). Computer Networks, Special Issue on Traffic Classification and Its Applications to Modern Networks 5 (6): 864–881.