What is an Intrusion Detection System? 

An intrusion detection system (or IDS) is a hardware device or software program that observers a network or system for security policy violations or malicious activity. Typically, any activity or intrusion violation is reported to either an administrator or is collected and logged in a central location using a security information and event management system (or SIEM) system. This system is a security-based technology developed initially for detecting exploits and vulnerabilities used against a computer or other target applications.

IDS systems are usually a passive system that monitors and reports issues that need to be investigated. This product differs from an Intrusion Prevention System (or IPS) in the sense that an IPS assumes an active role by monitoring and defending the system against threats. If a prospective danger is seen, the IPS quickly takes action to prevent any detected exploits from occupying and seizing the system.