National Security Information (NSI) is information that has been determined pursuant to Executive Order 12958 or any predecessor order to require protection against unauthorized disclosure and is marked to indicate its classified status when in documentary form. There are three classification levels of NSI. Each level is a measurement of the sensitivity of that information and the damage it could cause to the United States national security if disclosed. These are the only levels authorized for classified NSI:

TOP SECRET – Applied to information, the unauthorized disclosure of which reasonably could be expected to cause exceptionally grave damage to the national security that the original classification authority is able to identify or describe.

SECRET – Applied to information, the unauthorized disclosure of which reasonably could be expected to cause serious damage to the national security that the original classification authority is able to identify or describe.

CONFIDENTIAL – Applied to information, the unauthorized disclosure of which reasonably could be expected to cause damage to the national security that the original classification authority is able to identify or describe.

Additionally, there is a category of information known as “Sensitive Compartmented Information” (SCI), or “Codeword,” which is afforded more stringent protection because of its extreme sensitivity (U.S. Department of Justice, Security and Emergency Planning Staff, Classified National Security Information: Reference Booklet, June 1998, pp. 1 and 3).