This PAS establishes a framework for securing information and communication technology aspects of industrial process measurement and control systems including its networks and devices on those networks, during the operational phase of the plant’s life cycle. This PAS provides guidance on a plant’s operational security requirements and is primarily intended for automation system owners/operators (responsible for ICS operation) Furthermore, the operational requirements of this PAS may interest ICS stakeholders such as: a) automation system designers; b) manufacturers (vendors) of devices, subsystems, and systems; c) integrators of subsystems and systems. The PAS allows for the following concerns: • graceful migration/evolution of existing systems; • meeting security objectives with existing COTS technologies and products; • assurance of reliability/availability of the secured communications services; • applicability to systems of any size and risk (scalability); • coexistence of safety, legal and regulatory and automation functionality requirements with security requirements. NOTE 1 Plants and systems may contain safety critical components and devices. Any safety-related security components may be subject to certification based on IEC 61508 and according to the SILs therein. This PAS does not guarantee that its specifications are all or in part appropriate or sufficient for the security of such safety critical components and devices. NOTE 2 This PAS does not include requirements for security assurance evaluation and testing. NOTE 3 The measures provided by this PAS are rather process-based and general in nature than technically specific or prescriptive in terms of technical countermeasures and configurations. NOTE 4 The procedures of this PAS are written with the plant owner/operator\\\'s mind set. NOTE 5 This PAS does not cover the concept, design and implementation live cycle processes, i.e. requirements on control equipment manufacturer\\\'s future product development cycle. NOTE 6 This PAS does not cover the integration of components and subsystems into a system. NOTE 7 This PAS does not cover procurement for integration into an existing system, i.e. procurement requirements for owner/operators of a plant. NOTE 8 This PAS will be extended into a 3-part International Standard to cover most of the restrictions expressed in the previous notes; for the planned scope of the extended standards, refer to Annex A.