What is the primary function of firewalls in network security?

The primary function of firewalls in network security is to control incoming and outgoing network traffic based on predefined security policies. Firewalls act as a barrier between trusted internal networks and untrusted external networks (such as the internet) by enforcing rules that determine which traffic is allowed to pass through and which should be blocked. This capability helps to protect systems from unauthorized access, potential attacks, and harmful data transmissions, thereby maintaining the confidentiality, integrity, and availability of network resources.

Other functions like encrypting outgoing data, monitoring user internet usage, or automatically updating antivirus software do not accurately define the core purpose of a firewall. While encryption is important for securing data, it is not managed by a firewall. Monitoring user activity is typically the function of other security tools such as network monitoring solutions or proxy servers. Similarly, automatic updates of antivirus software are handled by the antivirus solution itself, not by a firewall. Thus, option B clearly encapsulates the essential role of firewalls in network security.