32 CFR 2400.9: Classification requirements.
(a) Information may be classified only if it concerns one or more of the categories cited in Executive Order 12356, as subcategorized below, and an official having original classification authority determines that its unauthorized disclosure, either by itself or in the context of other information, reasonably could be expected to cause damage to the national security.
(1) Military plans, weapons or operations;
(2) The vulnerabilities or capabilities of systems, installations, projects, or plans relating to the national security;
(3) Foreign government information;
(4) Intelligence activities (including special activities), or intelligence sources or methods;
(5) Foreign relations or foreign activities of the United States;
(6) Scientific, technological, or economic matters relating to the national security;
(7) United States Government programs for safe-guarding nuclear materials or facilities;
(9) A confidential source; or
(10) Other categories of information which are related to national security and that require protection against unauthorized disclosure as determined by the Director, Office of Science and Technology Policy. Each such determination shall be reported promptly to the Director of the Information Security Oversight Office.
(b) Foreign government information need not fall within any other classification category listed in paragraph (a) of this section to be classified.
(c) Certain information which would otherwise be unclassified may require classification when combined or associated with other unclassified or classified information. Classification on this basis shall be fully supported by a written explanation that, at a minimum, shall be maintained with the file or referenced on the record copy of the information.
(d) Information classified in accordance with this section shall not be declassified automatically as a result of any unofficial publication or inadvertent or unauthorized disclosure in the United States or abroad of identical or similar information. Following an inadvertent or unauthorized publication or disclosure of information identical or similar to information that has been classified in accordance with Executive Order 12356 or predecessor orders, OSTP, if the agency of primary interest, shall determine the degree of damage to the national security, the need for continued classification, and in coordination with the agency in which the disclosure occurred, what action must be taken to prevent similar occurrences. If the agency of primary interest is other than OSTP, the matter shall be referred to that agency.