Tenable Nessus

Tenable Nessus is the industry standard for vulnerability assessment. It is an essential tool for IT administrators and security professionals to identify misconfigurations, missing patches, and vulnerabilities across their network. With the largest library of vulnerability plugins in the industry, Nessus provides deep, accurate scanning capabilities. It is widely used for compliance auditing and ensuring that systems meet security benchmarks like CIS or HIPAA.

While it is not an active 'protection' tool, it is the foundation upon which a secure environment is built.