Intrusion Detection Systems (IDS) aim at detecting attacks against computer systems and networks or, in general, against information systems. Its basic aim is to protect the system against malwares and unauthorized access of a network or a system. Intrusion detection is of two type Network-IDS (NIDS) and Host based-IDS (HIDS). This paper covers the scope of both the types and their result analysis along with their comparison as stated. OSSEC (HIDS) is a free, open source host-base intrusion detection system. It performs log analysis, integrity checking, windows registry monitoring, rootkit detection, time-based alerting and active response.