The ISA/IEC 62443 series is structured into logical groups to address different aspects of industrial cybersecurity. Historically, the series was organized into Parts 1 through 4, covering general concepts, management system requirements, system requirements, and component requirements. As the standard evolved, the need arose to address sector-specific and application-specific cybersecurity needs without modifying the core requirements.

To address this, ISA introduced the concept of cybersecurity profiles. These profiles allow industries (such as oil and gas, power, water, or manufacturing) to select and tailor existing ISA/IEC 62443 requirements for their specific operational context while preserving consistency with the base standard.

The Profiles Group is formally designated as ISA/IEC 62443-5-x. This numbering clearly distinguishes profiles from foundational requirements and ensures that:

No new security requirements are created

Existing requirements are selected, scoped, and referenced appropriately

Alignment with Parts 2, 3, and 4 is preserved

By allocating profiles to the 5-x series, ISA ensures modularity and prevents fragmentation of the standard. Profiles serve as an application layer over existing requirements, enabling consistent adoption across sectors without redefining core security controls.

Parts 3-x and 4-x remain dedicated to system and component requirements, while 6-x does not exist in the published structure for profiles. Therefore, 5-x is the correct and formally defined answer.