Classified information is sensitive information to which access is restricted by law or regulation to particular classes of persons. A formal security clearance is required to handle classified documents or access classified data. The clearance process requires a satisfactory background investigation. There are typically several levels of sensitivity, with differing clearance requirements. This sort of hierarchical system of secrecy is used by virtually every national government. The act of assigning the level of sensitivity to data is called data classification.

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.

Government classification

The purpose of classification is ostensibly to protect information from being used to damage or endanger national security. Classification formalises what constitutes a "state secret" and accords different levels of protection based on the expected damage the information might cause in the wrong hands.

"I'm sorry, I don't speak German..." "I know a little German, He's sitting right over there"

(phone rings) -"Yeah? It is the hospital, Mein general !"

-"What is the condition of sergent Kruger?" Yes, I see... Well, let me know if there's any change in his condition..." (hangs up phone) "He's dead"

Hillary Flammond: "And I'll miss you most of all scarecrow."

Hillary Flammond: "Who do you favor in the Virginia Slims tournament?" Blindman: "In women's tennis, I always root against the heterosexual."

Blindman: "What phony dog poo?"

Dr Paul Flammond: "Go quickly. If they find out you've seen this, your life will be worth less than a truck load of dead rats in a tampon factory."