Official secret

Classified information is material that a government body claims is sensitive information that requires protection of confidentiality, integrity, or availability. Access is restricted by law or regulation to particular groups of people, and mishandling can incur criminal penalties and loss of respect. A formal security clearance is often required to handle classified documents or access classified data. The clearance process usually requires a satisfactory background investigation. Documents and other information assets are typically marked with one of several (hierarchical) levels of sensitivity—e.g. restricted, confidential, secret and top secret. The choice of level is often based on an impact assessment; governments often have their own set of rules which include the levels, rules on determining the level for an information asset, and rules on how to protect information classified at each level. This often includes security clearances for personnel handling the information. Although "classified information" refers to the formal categorization and marking of material by level of sensitivity, it has also developed a sense synonymous with "censored" in US English. A distinction is often made between formal security classification and privacy markings such as "commercial in confidence". Classifications can be used with additional keywords that give more detailed instructions on how data should be used or protected.

Some corporations and non-government organizations also assign sensitive information to multiple levels of protection, either from a desire to protect trade secrets, or because of laws and regulations governing various matters such as personal privacy, sealed legal proceedings and the timing of financial information releases.

With the passage of time much classified information becomes much less sensitive, and may be declassified and made public. Since the late twentieth century there has been freedom of information legislation in some countries, whereby the public is deemed to have the right to all information that is not considered to be damaging if released. Sometimes documents are released with information still considered confidential obscured (redacted), as in the example at right.

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