An Intrusion Detection System  is a security mechanism designed to monitor network traffic or system activity for signs of unauthorized access, misuse, or other malicious behavior. The IDS works by analyzing data traffic flowing through a network, comparing it to a database of known attack patterns or anomalous behavior, and raising an alert if it detects any suspicious activity.

There are two main types of IDS:

1. Host-based IDS (HIDS): A software application that monitors activity on a single host or endpoint device. HIDS typically use system logs and file integrity checks to detect anomalies and malicious activity.

2. Network-based IDS (NIDS): A hardware or software-based system that monitors traffic on a network segment or across the entire network. NIDS analyzes network traffic and compares it to a database of known attack patterns to identify malicious activity.