Nowadays it is very important to maintain a high level security to ensure safe and trusted communication of information between various organizations. Intrusion Detection System is a new safeguard technology for system security after traditional technologies, such as firewall, message encryption and so on. An intrusion detection system (IDS) is a device or software application that monitors network system activities for malicious activities or policy violations and produces reports to a Management Station. In this paper, we will look importance of IDS with different approaches. We have presented two types of AI system, both supervised and unsupervised.