What is a primary function of firewalls in securing networks?

Firewalls play a crucial role in network security by serving as a barrier between trusted internal networks and untrusted external networks, such as the internet. Their primary function is to prevent unauthorized access to networks. Firewalls achieve this by monitoring and controlling incoming and outgoing network traffic based on predetermined security rules. This helps protect sensitive information and system resources from potential attacks, intrusions, and unauthorized access.

By assessing traffic at various points, firewalls can block malicious packets, filter out harmful traffic, and ensure that only legitimate users have access to critical areas of a network. This capability is essential for maintaining the integrity and confidentiality of data, which is a core requirement laid out in the PCI DSS (Payment Card Industry Data Security Standard) for protecting cardholder information.

In contrast, other options do not accurately reflect the primary functions of firewalls. Increasing connection speed is not a purpose of firewalls, nor is data backup their responsibility. Additionally, while firewalls can protect both physical and virtual servers, their operation is not limited to just physical servers. Thus, the central function of firewalls in securing networks is focused on preventing unauthorized access, making this answer the correct choice.