Intrusion Detection System (IDS)

An intrusion detection system (IDS) is a type of security software designed to automatically alert administrators when someone or something is trying to compromise information system through malicious activities or through security policy violations.

An IDS works by monitoring system activity through examining vulnerabilities in the system, the integrity of files and conducting an analysis of patterns based on already known attacks. It also automatically monitors the Internet to search for any of the latest threats which could result in a future attack.

There are a multiple ways detection is performed by an IDS. In signature-based detection, a pattern or signature is compared to previous events to discover current threats. This is useful for finding already known threats, but does not help in finding unknown threats, variants of threats or hidden threats.
Another type of detection is anomaly-based detection, which compares the definition or traits of a normal action against characteristics marking the event as abnormal.

There are three primary components of an IDS:

• Network Intrusion Detection System (NIDS): This does analysis for traffic on a whole subnet and will make a match to the traffic passing by to the attacks already known in a library of known attacks.
• Network Node Intrusion Detection System (NNIDS): This is similar to NIDS, but the traffic is only monitored on a single host, not a whole subnet.
• Host Intrusion Detection System (HIDS): This takes a “picture” of an entire system’s file set and compares it to a previous picture. If there are significant differences, such as missing files, it alerts the administrator.