Classified information is secret information to which access is restricted by law or corporate rules to a particular hierarchical class of people. A security clearance is permission to handle classified documents or class of information, often requiring a satisfactory background check. This sort of hierarchical system of secrecy is used by virtually every national government, and by many corporations as well.
The purpose of classification and secrecy is to protect information from being used to damage (or endanger) national security objectives. In the United States, information cannot be classified merely because it would be embarrassing; information can only be classified in relationship to protecting national security objectives of the state.
U.S. Government's Classification system
Most of the information about clearances and classification relates to the United States Government classification systems established by the Director of Central Intelligence — utilized under Executive Order 13292 (amending EO 12958) issued by President George W. Bush in 2003; this executive order lays out the system of classification for information handled by the United States Government and its employees, contractors, and industrial firms, handling classified information.
The desired degree of secrecy about such information is known as its sensitivity. Sensitivity is based upon a calculation as to the damage to "national security". The United States has three levels of classification — confidential, secret, and top secret. Each level of classification indicates an increasing degree of sensitivity — top-secret being the highest, and confidential being the lowest. If one holds a "top-secret" clearance, one is allowed to handle information up to the level of "top-secret" (thus, secret, and confidential information). If one holds a "secret" clearance, one may not then handle "top-secret" information, but may handle confidential classified information.
Accessing Classified Information
In addition to this, information that is classified is often restricted in its dissemination based on the "need to know." In order to have access to classified information in the U.S. government, one must have both the proper degree of classified clearance as well as a need to know the information. Having a "top-secret" clearance does not give one access to all documents classified at that level. Rather, information is released/disseminated based upon sensitivity level and the need to know. In addition, dissemination of information is often compartmentalized, requiring special additional clearance requirements above the "collateral" clearance (confidential, secret, and top-secret are collateral clearance levels). For example, individuals who need access to the most sensitive information, as well as information that is highly restricted in its dissemination, hold a "TS/SCI" clearance — Top-Secret/Sensitive Compartmental Information. In addition, specialized programs or "SAPs" (Special Access Programs) may restrict access to ALL information relating to a specific program or project — regardless of its classification.
Classified vs. Unclassified Information
Such information is called "classified" because it falls into a certain classification of secrecy. Information which is not restricted is called unclassified information. In general use, "unclassified" often refers to information which has recently had its classification removed, thus the media may speak of an "unclassified report." Information which was never classified is generally referred to as "open source," by those who work in national security.
Levels of Classification used by the U.S. Government
The United States Government classifies information according to the degree which the unauthorized disclosure would damage national security:
- Top secret – this is the highest security level, and is defined as information which would cause "exceptionally grave damage" to national security if disclosed to the public. Despite public mystique, relatively little information is classified at "Top Secret" (when compared to the other levels of classification). Only that which is exceptionally sensitive (weapon design, presidential security information, nuclear-related projects, various intelligence information) is classified at the Top Secret level.
- Secret – the second highest classification. Information is classified secret when its release would cause "serious damage" to national security. By far, most information that is "classified" is held at the secret sensitivity.
- Confidential – is the lowest classification level. It is defined as information which would "damage" national security if disclosed.
- Unclassified – not technically a "classification", this is the default, and refers to information which can be released to individuals without a clearance. Information that is unclassified is sometimes "restricted" in its dissemination, although such restrictions are generally meaningless. For example, the "law enforcement bulletins" often reported by the U.S. media when United States Department of Homeland Security raises the U.S. terror threat level are usually classified as "U//LES" or "Unclassified - Law Enforcement Sensitive." This information is only supposed to be released to Law Enforcement groups (Sheriff, Police, etc.) Because the information is unclassified, however, it is often released to the public as well. Information which is unclassified, but which the government does not believe should be subject to Freedom of Information Act requests is often classified as U//FOUO - Unclassified-For Official Use Only.
Proper procedures for classifying U.S. government documents
Classified U.S. government documents are required to be stamped with their classification at the top and bottom of each page. In addition, to be properly classified, a classification authority (an individual charged by the Government with the right and responsibility to properly determine the level of classification and the reason for classification) must determine the appropriate classification level as well as the reason information is to be classified. Executive Order 13292, signed by President Bush in 2003, describes the reasons and requirements for information to be classified. Classification restrictions are generally promulgated by the Director of Central Intelligence and adopted throughout the U.S. government.
There are also compartments, or "code words", which pertain to specific projects, and are used to more easily manage which individuals require certain information. Code words are not levels of classification themselves, but a person working on project X may have the code word for that project added to his file, and then will be given access to the relevant documents. Code words may also label the sources of various documents; for example, there are code words used to indicate that a document may break the cover of intelligence operatives if its content becomes known. The WWII code word ULTRA identified information found by decrypting German ciphers, such as the Enigma machine, and which — regardless of its own significance — might inform the Germans that Enigma was broken if they became aware that it was known. In the United States Department of Defense, compartmentalized information is usually classified at Top Secret levels, but with the additional caveat of being Sensitive Compartmentalized Information or SCI.
The United States also has a system of "restrictions" which can be added to a document; these are constantly changing, but can include (in abbreviated form) a requirement that the document not be shared with civilian contractor, or not leave a specific room. Technically, one violating these directives would be guilty of violating a lawful order — not the laws pertaining to the levels of classification — and most of these designations do not appear in written law at all. Some of these include NOFORN, meaning no distribution to foreign nationals, NOCONTRACTOR, meaning no distribution to contract personnel, and FOUO, or For Official Use Only. These restrictions are not classifications in and of themselves, rather, they restrict the dissemination of information within those who have the appropriate clearance level and possibly the "need to know" the information. The most common restrictions used are FOUO, NOFORN, and in the State Department SBU (sensitive but unclassified). Remarks such as "eyes only" also limit the restriction. When used alone, these descriptions have little meaning without a collateral classification (confidential, secret, top-secret) marking.
Classifications and clearances between U.S. government agencies
It is also important to note that classifications and clearances do not necessarily transfer between various U.S. government agencies. For example, an individual cleared for Department of Defense Top Secret must undergo another investigation before being granted a Department of Energy Q clearance. However, if one holds a Top Secret clearance at one agency, it is often possible (and practicable) to "pass" one's clearance to another agency. For example, officials visiting at the White House from other government agencies technically must "pass" their clearances to the EOP (executive office of the President). This is because most security clearances are licenses only to handle sensitive information inside the agency with whom they work. The discussion of classified information outside one's agency requires the verification to handle such classified materials — this process of verification is "passing clearances."
Other levels of classification some claim to exist
Various UFO conspiracies mention a level "above top secret" used for UFO design information and related data. They suggest such a classification is intended to apply to information relating to things whose possible existence is to be denied, such as aliens, as opposed to things whose potential existence may be recognized, but for which access to information regarding specific programs would be denied as classified. The existence of an “above top secret” classification is considered by some as unnecessary to keep the existence of aliens a secret, as they say Information at the "Top Secret" level, or any level, can be restricted on the basis of need-to-know. Thus, the U.S. Government could conceal an alien project without having to resort to another level of clearance. The "need to know" would limit the ability to have access to the information. Some suggest that claims of the existence of such a classification level may be based on the mistaken belief that the ‘’levels’’ of classification are themselves classified: As such they feel that books available claiming to contain "above top secret" information on UFOs or remote viewing should arguably be taken with a grain of salt.
Clearances that are not classifications
Naval Nuclear Propulsion Information
While most Naval Nuclear Propulsion Information is sensitive, it may or may not be classified. The United States Navy recognizes that the public has an interest in environmental, safety, and health information, and that the basic research the Navy carries out can be useful to industry.
Yankee White Clearance
Contrary to popular lore, the Yankee White clearance given to personnel who work directly with the President is not a classification. Individuals having Yankee White clearances undergo extensive background investigation. Yankee White cleared personnel are granted access to any information for which they have a need-to-know, regardless of which organization classified it or at what level. 
Classification of information between countries
When a government agency or group shares information between an agency or group of other country’s government they will generally employ a special classification scheme which both parties have previously agreed to honor. For example, information shared amongst NATO allies, the classification of NATO SECRET & COSMIC TOP-SECRET exists to protect information used by them. In cases where the United States wishes to share classified information bilaterally (or multilaterally) with a country that has a sharing agreement, the information is marked "REL" (release) and the three-letter country code. For example, if the U.S. wanted to release classified information to the governments of France, UK, and Canada, it would mark the document "REL FRA, GBR, CAN." Those countries would have to maintain the classification of the document at the level originally classified (SECRET, TOP-SECRET, etc.). The United States has military and national security information sharing agreements with most of its allies.
Trusted operating systems
Specialized computer operating systems known as trusted operating systems are available for processing classified information: they enforce the classification and labeling rules described above in software.
Claims of U.S. government misuse of the classification system
While the classification of information by the government is not supposed to be used to prevent information from being made public that would be simply embarrassing or reveal criminal acts, it has been alleged that the government routinely misuses the classification system to coverup misdeeds. Many conspiracy theories such as the JFK assassination theories suggest that the government has classified information as top secret that reveals the involvement of agencies such as the CIA.
Incomplete list of terms used to indicate type, level, or scope of clearance in USA
- 1C or 2C - Federal
- 3C or 4C - Federal
- 5C or 6C - Federal
- ADP 1
- ADP 2
- CIA Lifestyle Polygraph
- Cosmic Top Secret - ATOMAL/CTSA
- DEA Clearance
- DOD Lifestyle Polygraph
- DOD Secret
- DOD - Top Secret SSBI
- DOE - Nuclear
- DOE - C
- DOE - L
- DOE - Q
- DOJ � NACI
- DOJ - Sensitive
- DOJ - Secret
- DOJ - Top Secret
- EBI - Extended Background Investigation
- FAA Clearance
- Foreign Government Information
- Industrial Clearance
- Inactive Clearance
- Inactive Top Secret Crypto
- Interim Secret
- Interim Top Secret
- Interim TS / SCI
- IRS - MBI
- ISSA / CISSP
- MBI (IRS)
- NATO Secret
- NSA Lifestyle Polygraph
- Position of Public Trust 1C
- Position of Public Trust 2C
- Position of Public Trust 3C
- Position of Public Trust 4C
- Position of Public Trust 5C
- Position of Public Trust 6C
- Polygraph - Counterintelligence
- Polygraph - Full Scope / Lifestyle
- S - Secret
- Secret COMSEC
- Secret SBI
- SIDA - Secured Identification Defense Area
- SAP - Special Access Programs
- SBI - Special Background Investigation
- SCI - Special Compartmented Intelligence
- SSBI - Single Scope Background Inv.
- TS - Top Secret
- Top Secret-Crypto
- Top Secret-Crypto SCI / TK / G / HCS-P
- Top Secret-Final / Crypto / Polygraph
- Top Secret-SCI / SBI
- Top Secret-SCI / HSC
- Top Secret-SCI / SI / TK
- Top Secret-SCI / SI / TK / G / B
- Top Secret-SCI / SI / TK / G / HCS
- Top Secret-SCI / SIOP
- Top Secret-SCI / SSBI
- Top Secret-SBI-TS/SBI
- Top Secret-CISP-TS/CISP
- Top Secret-ISSA-TS/ISSA
- Top Secret-SAP-TS/SAP
- Top Secret-SCI-CI polygraph-TS/SCI/CI Poly
- Top Secret-SCI-Full/Scope Lifestyle-TS/SCI Lifestyle Poly
- Top Secret-SCI-TS/SCI
- Top Secret-SSBI-TS/SSBI
- Top Secret-SCI /SSBI / SI / TK
- Top Secret-SCI / TK / G / HCS / CI Poly
- Top Secret-SCI / TK / G / Lifestyle Poly
- Top Secret-SCI / SSBI / CI Poly
- Top Secret-SI / TK / B / +
- Top Secret-SSBI / CI Poly
- Top Secret-SSBI / SCI / TK / G / HCS
- Top Secret-SSBI / Lifestyle Poly
- Top Secret-SSBI / SCI
- Top Secret-SSBI / SCI/ SI / TK / G
- Top Secret-SSBI / SCI / SI / TK / G / B / HCS
- Top Secret-SSBI / SCI / TK / HCS
- Top Secret-SSBI / SCI-B
- Top Secret-EBI
- Top Secret-SCI - SI / TK / G / HCS / I / P
- Top Secret-CISP - TS / CISP
- Top Secret-ISSA - TS / ISSA
- Top Secret-SAP - TS / SAP
- Top Secret-SCI - CI Poly - TS / SCI / CI Poly
- Top Secret-SCI - Full / Scope Lifestyle - TS / SCI Lifestyle
- Top Secret-SCI - TS / SCI
- Top Secret-SSBI - SCI / TK / B / HCS / CI - Poly
- Top Secret-SSBI - TS / SSBI
- US Citizen
- US Customs
- US Treasury Clearance
- Yankee Fire
- Yankee White