How can an administrator harden a server by removing unnecessary FTP services without causing disruption?

Removing unnecessary FTP services from a server is an important step in hardening it against potential security threats. Disabling ports associated with FTP services effectively minimizes the attack surface of the server. In this context, by closing the specific ports that FTP uses, an administrator can prevent unauthorized access and mitigate risks without disrupting other necessary services or functionalities on the server.

This approach is non-intrusive as it does not require changing the server's interfaces or configurations that other services might rely on. Disabling ports can be done without affecting users who need access to other services, thereby maintaining overall system stability while increasing security.

In contrast, other options such as disabling interfaces might inadvertently affect network connectivity, enabling encryption does not directly address the removal of FTP services, and reviewing user accounts, while a good security practice, does not directly relate to the specific action of hardening the server by removing unnecessary services like FTP.