What is the purpose of a firewall?

The purpose of a firewall is to monitor and control incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between a trusted internal network and untrusted external networks—such as the internet. By filtering traffic, firewalls can block unauthorized access while allowing legitimate communication to pass through. This function is crucial for protecting information systems from cyber threats, unauthorized access, and other malicious activities.

Other choices do not accurately capture the firewall's role. Encrypting sensitive data is a function of encryption technology, which secures data by transforming it into an unreadable format for unauthorized users. Preventing all foreign traffic is not practical or effective; firewalls aim to selectively permit or deny traffic based on specific criteria rather than completely shutting out external access. Additionally, while some firewalls may have integrated capabilities to detect viruses, their primary function is not focused on virus detection, but rather on managing traffic to regulate security.