Which of these refers to the software that protects the system from unauthorized access?

The software that protects the system from unauthorized access is indeed a firewall. A firewall acts as a barrier between a trusted internal network and untrusted external networks, such as the internet. It monitors and controls incoming and outgoing network traffic based on predetermined security rules. By doing so, it helps prevent unauthorized access to or from the network, protecting sensitive data and resources from threats.

In contrast, antivirus software is designed to detect and remove malicious software (malware) from systems but does not specifically block unauthorized access at the network level. Malware refers to any malicious software designed to harm or exploit devices, networks, or services. Encryption is a method of securing data by converting it into a coded format that can only be read with a specific key or password; while it protects data integrity and confidentiality, it does not serve the purpose of controlling access to systems.