Classified information

Classified information is material, collected or created by a government, that is subject to limitations on its release to the general public, has restrictions on its handling based on security concerns, and may have penalties for its unauthorized release. The general assumption is that the inappropriate disclosure of such information could do varying levels of harm to the national security of a nation, including diplomatic, military, and intelligence missions.

Other governmental information, including civilian law enforcement, privileged business information, personnel matters, medical records, etc., may have restrictions on access and distribution, but the term "classified" tends to be specific to national security. Also, businesses may have material that is "proprietary" and safeguarded internally as is classified material; governments may receive proprietary information and will be expected, within legal requirements, to protect it from disclosure. See the National Industrial Security Program Operating Manual for United States examples of safeguarding measures.

Levels of sensitivity

General classification

Most countries have between two and five increasingly stringent levels of classification based on the harm that disclosure is predicted to cause. With increasing level, there will be more and more physical protection, more investigative requirements for security clearances to handle the material, and, in general, more restricted distribution.

A multinational hierarchy consists of (in the appropriate language), the following general levels:

Typical descriptor	General sensitivity
UNCLASSIFIED	Releasable to the public
FOR OFFICIAL USE ONLY; SENSITIVE BUT UNCLASSIFIED	Restricted but not technically classified. For example, it might be used to give law enforcement and public safety organizations, which are not authorized to received classified material, warning of terrorist threats
RESTRICTED	No longer used by the U.S. but in NATO practice, for national security information that might do slight damge if released
CONFIDENTIAL	Capable of doing some harm, such as the ballistics of a specific gun, which would become obvious in battle
SECRET	Expected to cause serious damage if leaked; probably the most common level
TOP SECRET	If disclosed, would be likely to cause critical damage. Material at this level, besides such things as immediate military plans, often falls into the next level
TOP SECRET-CODEWORD	TOP SECRET with additional restrictions for issues such as intelligence sources and menthods, detailed design of nuclear weapons, etc.

Supplementary classification

For certain kinds of data, there may be a supplemental system that either is considered parallel to or additive with the general classification system. See compartmented control system for practices in the U.S., which are fairly closely reflected in the systems of Australia, Canada, New Zealand, and the United Kingdom. Such material may also receive special and limited handling in NATO and other alliance.

Protection

Classified material must itself have physical protection, and people who are authorized access to it must be checked for trustworthiness. U.S. classified material cannot be transmitted by electronic means that lack encryption. For example, the U.S. SIPRNET network provides Internet Protocol transmission for material up to and including SECRET. Telephones that provide encryption are needed to discuss classified material.

Security clearance

Individuals are granted the privilege of access to a given level of classified material after an investigation and adjudication process variously called an background investigation or positive vetting. The possession of the clearance, however, rarely conveys the right to see all information of that classification; the principle of need to know applies: a submarine captain will have a high security clearance, but security officials might be alarmed if the captain wanted access to the details of a communications technique used purely by ground special operations personnel.

Controversies

Classification is sometimes improperly used to conceal embarrassing information whose disclosure might hurt politically, but not damage the true security.