What security measure is recommended for unused ports?

Turning off unused ports is an essential security measure because open ports can serve as potential entry points for attackers. Many cyber-attacks exploit open ports to gain access to systems or networks, making it crucial to limit exposure by ensuring that only necessary ports are active. When ports are not in use, disabling them reduces the attack surface, thereby minimizing vulnerabilities that could be exploited by malicious actors.

By not allowing unused ports to remain open, organizations can enhance their security posture. This practice aligns with the principle of least privilege, which recommends limiting access rights for accounts and systems to the bare minimum permissions they require to function.

The other options are less secure; leaving ports open invites unnecessary risk, using them for low-risk applications may still expose the system to threats, and merely monitoring unused ports does not mitigate the potential danger of exploitation. Thus, turning off unused ports is the most effective method to protect against unauthorized access and attacks.