Annex A.13 Communications Security protects information and information systems from unauthorised access or modifications. A system's effectiveness is measured by how well it accomplishes its objectives while still preserving the ability to produce useful output.
It is an important part of the ISMS (Information security management system) which covers all areas where the organisation is at risk of security breaches. This also applies to any third party that interacts with the organisation's IT systems.
This blog discusses communications security (COMSEC), its controls, and the importance of protecting information and information systems from unauthorised access or modification.