Final answer:
To securely copy files to a Linux host with an SSH server, SCP is commonly used because it encrypts data transfers. Rsync can also be secure when used with SSH, unlike FTP and Telnet, which are not secure.
Step-by-step explanation:
To securely copy files to a Linux host running the SSH server daemon, the program you would use is SCP (Secure Copy Protocol). SCP uses the SSH protocol for data transfer and provides the same level of security, ensuring that sensitive data is transmitted in an encrypted form over a network. While FTP is used for file transfer as well, it does not encrypt its data and is thus not secure.
Rsync can also be used for copying files and does support encryption when used with SSH. However, without additional configuration, rsync uses its own protocol over port 873 and wouldn't be secure by default. Lastly, Telnet is an outdated protocol that sends data in plaintext and should not be used for secure data transfer.
The use of SCP or Rsync with SSH will ensure your files are transferred securely, protecting them from interception or eavesdropping, which is critical when handling sensitive information.