Which service is NOT considered secure for use in system operation?

• A. Telnet
• B. SSH
• C. HTTPS
• D. SFTP

Answer: (A)

The essential idea is that remote-management services must protect data in transit to keep credentials and commands from being exposed. Telnet does not encrypt traffic; login credentials and session data travel in plaintext, so anyone on the network path can eavesdrop, capture passwords, or tamper with the session. This makes it unsuitable for secure system operation.

In contrast, SSH provides a secure, encrypted channel for remote administration, so credentials and commands are protected from interception. HTTPS encrypts web traffic with TLS/SSL, safeguarding data between clients and servers. SFTP also runs over SSH and offers encrypted file transfers, protecting both the transfer and control information. Because of these protections, Telnet is considered insecure for system management, while SSH, HTTPS, and SFTP are the secure alternatives.