An Intrusion Detection System (IDS) is designed to detect attempts to break into or misuse a computer system. It monitors network traffic for suspicious activity and alerts administrators when such activities are detected. It does not act as a physical or preventative lock on systems (as in option A), nor is it capable of blocking traffic (as in option C). While it helps identify vulnerabilities when they are exploited, it is not effective against all vulnerabilities (as in option B).