Which of the following is used to protect a computer from unauthorized access over a network?

Correct option is B

A firewall is used to block unauthorized access to a computer or network while allowing legitimate communication.

Important Key Points:
Firewall: Prevents unauthorized access. Critical in both hardware and software form, they are essential for network security.​
Knowledge Booster:
Antivirus: Protects against malware.
Worm: A self-replicating malware.
Trojan: Malicious software disguised as legitimate.
Router: Manages network traffic, but not for protection.​