1. INTRODUCTION In the 1950s, computer networks became the core of communication in military radar systems and evolved such that approximately 9 billion devices are currently connected via the Internet. The computer network is currently used for business and personal use. However, these connections between devices are misused by attackers in the form of Internet attacks. These attacks represent an ever-growing threat to the Internet that must be defended by a security defense system. The factors that a security system should provide are integrity, confidentiality and availability. Intrusion detection system is one of them, which monitors network traffic for possible attacks and reacts by alarming the security officer or performing any custom action. Currently, a lot of research is being conducted in this area and it has been seen that artificial intelligence plays an important role and works effectively in the development of this type of system. Therefore, the objective of this paper is to describe the methods and areas of artificial intelligence used in different types of intrusion detection systems. We will elaborate commonly used artificial intelligence algorithms and detection principles.2. INTRUSION DETECTION SYSTEM OVERVIEW 2.1 Network Attacks There are four main categories of attacks: Denial of Service (DOS): is an attack that makes the attacked machine busy so that it is unable to serve legitimate clients (e.g. Apache, smurf, neptune, ping to death etc.). Remote User Attacks (R2L): It is an attack in which the attacker sends packets to a host machine, which he does not have access to, exploiting vulnerabilities and having control over that host system by having access to the host user's privileges. (e.g.... half of the paper ......r intrusion detection.”, Systems, Applications and Technology Conference, 2006. LISAT 2006. IEEE Long Island pp.1-8.[8] Aida O. Ali , Ahmed I. saleh and Tamer R. Badawy “Intelligent Adaptive Intrusion Detection Systems Using Neural Networks” International Journal of Video and Image Processing and Network Security IJVIPNS-IJENS Vol:10 No:01, pp.1- 8[9] Mohammad Sazzadul Hoque, Md. Abdul Mukit, Md. Abu Naser Bikas “An implementation of intrusion detection system using genetic algorithm.” International Journal of Network Security & Its Applications (IJNSA), Vol.4 , No.2, March 2012, pp.109-120[10] Anshuman Sharmaa and MR Aloneb “A New Approach to Improve Detection Rate in Intrusion Detection System Using Multilayer Perceptron Algorihtm” Information Sciences and Computing Volume 2013, Number 1, pp.1-7[11] http://www.sans.org/security-resources/idfaq/switched3.gif