What is included in the merchant's infrastructure?

The merchant's infrastructure is a comprehensive term that encompasses all components necessary for storing, processing, and transmitting cardholder data in a secure manner. This consists not only of application software but also includes networking and operating systems, as well as critical components such as firewalls and routers. These elements work together to create a secure environment that protects sensitive data and ensures compliance with the PCI DSS requirements.

Networking and operating systems form the backbone of the merchant's infrastructure, enabling communication and facilitating the operation of applications that handle payment information. Firewalls and routers are essential for establishing secure boundaries, controlling access to network segments, and protecting against unauthorized access and threats. The integration of these components is vital for maintaining a secure payment system.

In contrast, the other options focus on only one aspect of the infrastructure, whether it be application software, physical security devices, or third-party management tools and platforms. While each of these is important in its own right, they do not represent the full scope of what constitutes a merchant's infrastructure for PCI DSS compliance, which requires a holistic view of security that includes all layers of technology and controls.