U.S. presidents have leaked sensitive information to influence public opinion. Typical classification levels Although the classification systems vary from country to country, most have levels corresponding to the following British definitions (from the highest level to lowest). Top Secret (TS) Top Secret is the highest level of classified information. Information is further compartmented so that specific access using a code word after top secret is a legal way to hide collective and important information. Such material would cause "exceptionally grave damage" to national security if made publicly available. Prior to 1942, the United Kingdom and other members of the British Empire used Most Secret, but this was later changed to match the United States' category name of Top Secret in order to simplify Allied interoperability. The Washington Post reported in an investigation entitled "Top Secret America" that, as of 2010, "An estimated 854,000 people ... hold top-secret security clearances" in the United States. Secret Secret material would cause "serious damage" to national security if it were publicly available. In the United States, operational "Secret" information can be marked with an additional "LimDis", to limit distribution. Confidential Confidential material would cause "damage" or be prejudicial to national security if publicly available. Restricted Restricted material would cause "undesirable effects" if publicly available. Some countries do not have such a classification in public sectors, such as commercial industries. Such a level is also known as "Private Information". Official Official (equivalent to US DOD classification FOUO – For Official Use Only) material forms the generality of government business, public service delivery and commercial activity. This includes a diverse range of information, of varying sensitivities, and with differing consequences resulting from compromise or loss. Official information must be secured against a threat model that is broadly similar to that faced by a large private company. The Official Sensitive classification replaced the Restricted classification in April 2014 in the UK; Official indicates the previously used Unclassified marking. Unclassified Unclassified is technically not a classification level. Though this is a feature of some classification schemes, used for government documents that do not merit a particular classification or which have been declassified. This is because the information is low-impact, and therefore does not require any special protection, such as vetting of personnel. A plethora of pseudo-classifications exist under this category. Clearance Clearance is a general classification, that comprises a variety of rules controlling the level of permission required