The answer to question 01: Any password that is simple to guess, especially if the guessing is done by a password cracking machine. Names, birthdays, vehicle registrations, sequential number strings, and, of course, the term "password" are some of the most frequent passwords. The answer to question 02: Access Control List (ACL) enforced by firewall. Also prescanning tools The answer to question 03: Telnet is not a secure protocol and is unencrypted. By monitoring a user's connection, anyone can access a person's username, password, and other private information that is typed over the Telnet session in plaintext.