The King may issue regulations on the identification and protection of critical national information. In special cases, such regulations may grant exemptions from security requirements specified in or pursuant to this act. Section 5-3.Classified information An undertaking which produces information shall classify and mark the information if national security interests may be harmed if the information becomes known to unauthorised persons. The following security classification levels shall be used: a) TOP SECRET if critical adverse consequences could result b) SECRET if serious adverse consequences could result c) CONFIDENTIAL if adverse consequences could result d) RESTRICTED if adverse consequences could result to some extent. Security classification shall not be used to a greater extent or for longer than necessary. Unless otherwise provided, the security classification shall cease to apply after 30 years. The King may issue regulations on security classification and protection of information received or provided pursuant to a mutually binding agreement with a foreign state or international organisation. Section 5-4.Access to and duty of secrecy in respect of classified information Classified information shall only be released to persons who have an official need-to-know and are authorised to have access to such information. All persons who have access to classified information as part of their work or service for an undertaking covered by the act have a duty of secrecy in respect of the content of such information. The duty of secrecy continues to apply after such work or service has concluded. Section 5-5.Technical surveillance countermeasures The National Security Authority may inspect premises, buildings and other objects which an undertaking controls either alone or together with other parties to determine whether unauthorised persons could gain access to classified information through wiretapping, physical observation or signal interception. Information gathered during such an inspection may only be used for the purpose of the inspection. The information shall be erased when it is no longer needed. Knowledge and experience acquired by the National Security Authority through the inspection may be 10/30