Classified information is data which, for one reason or another, has been deemed to require certain
security measures to protect the range of its disclosure. Often, the viewing of such information by an individual requires that the person undergo a
background check[?]; after this is satisfactorily completed, he or she is then issued a
security clearance.
It is often the case that sensitive information is disseminated on the basis of a need to know, which is to say if an individual needs to know certain information in order to satisfactorily perform her or his function in the organization, their viewing of that information is authorized, otherwise it is not.
Such information is called "classified" because it falls into a certain classification of sensitivity. This sort of hierarchical system is used by virtually every national government, and by many corporations as well. The United States government, for example, has a formal hierarchy of classification for sensitive data:
- Top secret – this is the highest security level, and is defined as information which would cause "severe" damage to national security if disclosed to the public. This classification is most often subdivided on the basis of "need to know", and includes such information as the design of cutting-edge weaponry, etc.
- Secret – the second highest classification may include, for example, details of other security measures and procedures. It is defined as information which would cause "serious" damage to national security if disclosed.
- Confidential – the classification of information which is exempt from disclosure under the Freedom of Information Act and other such laws, and can include such things as results of the background checks mentioned above. It does not involve considerations of national security.
- Sensitive but Unclassified (SBU) – data which is not related to national security but whose disclosure to the public could cause some harm; such data includes personal demographic information from recent censuses, for example.
- Unclassified – this is the default classification for data, and refers to information that is not sensitive and can be freely disclosed to the public. Information which was previously classified under one of the above levels is often declared "unclassified" at a certain time because its age has made its classification no longer necessary.
Classified U.S. government documents are required to be stamped with their classification at the top and bottom of each page, and there are various other regulations for the handling and storage of such documents.
The classification scheme of course varies between organizations; for example, in Canada information which the U.S. would classify SBU is called "protected," and further subcategorized into levels A, B, and C.