An Intrusion Detection System (IDS) is a security tool that monitors and analyzes network traffic for malicious activity. It is designed to detect malicious activities such as unauthorized access, malicious code, or malicious data.
For example, an IDS can detect a port scan attack, which is a common attack in which a malicious actor scans a network for open ports. The IDS will detect the port scan and alert the network administrator, who can then take action to prevent further damage. The IDS can also detect other malicious activities such as malicious code, buffer overflows, and denial of service attacks.