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Abstract

abnormal circumstances while monitoring the systems and target to take the necessary precaution. Attack detection mechanisms used by IDS are basically divided into two. These are signature-based methods and anomaly based methods. Signature-based methods are used more for known intrusion types prevalently. Anomaly based methods model the normal behavior of the network and determines abnormal circumstances through the obtained model of normal state. Anomaly based methods are preferred more as they are more successful than the signature-based model in terms of detecting the new intrusion types. Anomaly detection systems determine behaviors that show deviation from the expected normal usage profiles as an anomaly. In the detection of the anomaly the normal behavior of the system is generally obtained using the statistical methods. One of the statistical methods used generally for this purpose is the Hidden Markov Model (HMM). Markov model is used to represent the tiered observations happen in time. HMM is a special version of the Markov