* A brute-force attack is a type of attack that tries to guess the user's password by systematically trying all possible combinations of characters until the correct one is found12.
* A brute-force attack can be performed by an attacker who has physical access to the user's computer or by a remote attacker who can intercept the user's network traffic or access the user's online account12.
* A brute-force attack can prevent the user from logging in after locking the computer, as the attacker may have changed the password or locked the account after guessing the password12.
* Therefore, option A is the correct answer, as a brute-force attack is the most likely attack against the user in this scenario.
* The other options are incorrect, as they are not likely to cause the user's login problem.
* Option B is incorrect because an on-path attack (also known as a man-in-the-middle attack) is a type of attack that intercepts and modifies the user's network traffic without the user's knowledge12. An on-path attack can compromise the user's data or credentials, but it does not prevent the user from logging in after locking the computer, unless the attacker also performs a brute-force attack12.
* Option C is incorrect because a deauthentication attack is a type of attack that disconnects the user from a wireless network by sending spoofed deauthentication frames to the user's device or the access point12. A deauthentication attack can disrupt the user's network connectivity, but it does not prevent the user from logging in after locking the computer, unless the user needs to authenticate to the wireless network again12.
* Option D is incorrect because a phishing attack is a type of attack that tricks the user into revealing sensitive information or clicking malicious links by sending fraudulent emails or messages that appear to be from legitimate sources12. A phishing attack can compromise the user's data or credentials, but it does not prevent the user from logging in after locking the computer, unless the user falls for the phishing attempt and changes the password or clicks a malicious link that performs a brute-force attack12.
References:
* : CompTIA Network+ N10-008 Study Guide, Chapter 6, Section 6.1, "Common Network Attacks", page 308-310.
* : Professor Messer's CompTIA N10-008 Network+ Course Notes, Section 6.1, "Common Network Attacks", page 46-47.