Protective software, such as a firewall, is a type of computer program designed to protect computers and networks from malicious attacks. Firewalls are used to block unauthorized access to a network or system, and can be either hardware- or software-based. They are typically configured to allow only certain types of traffic to pass through, while blocking all other traffic. Firewalls can also be used to monitor and log activity on a network, providing an additional layer of security.