Which tool is used for network discovery tasks and security auditing, providing a way to assess systems and software running in a networked environment?

The tool used for network discovery tasks and security auditing that provides a way to assess systems and software running in a networked environment is a port scan. A port scan is a technique employed to identify open ports and active services on a system or network. By sending network requests to various ports, a port scanner can determine which ports are accepting connections, giving insight into the network's configuration and potential vulnerabilities.

Port scanning aids in understanding the systems running within the network and helps security professionals identify misconfigurations or unauthorized services that could pose security risks. This technique is foundational for assessing the security posture of systems and ensuring that appropriate measures are in place to protect against potential attacks.

The other options, while useful in their own contexts, do not specifically focus on discovering open ports and active services in the same way that a port scan does. For example, security content automation protocols are typically used for automating compliance and security assessment rather than direct network discovery. Vulnerability scans assess known vulnerabilities within systems but do not inherently provide detailed information about network services. A protocol analyzer captures and analyzes data packets but is typically more concerned with the data being transmitted rather than identifying possible services on a network. Thus, for network discovery and security auditing, a port scan is the most appropriate