The answer to question 01: Telnet. The answer to question 02: Providing a secure terminal to a remote Linux or UNIX computer is the most common use (or any other host with an SSH server installed). The answer to question 03: Pass-the-Hash (PtH) attacks are a type of attack. The attacker obtains credentials via an RDP session with the RDP server and attempts to re-use them in PtH. Credential Guard is intended to keep the password hash from being stored or processed by the RDP server.