The best way to prevent the disclosure of classified documents printed on a shared printer is to require a key code to be entered on the printer to produce hard copy. This key code should be known only by authorized personnel, and should be changed frequently to prevent unauthorized access. Other methods such as using passwords to allow authorized users to send documents to the printer, encrypting the data stream between the user's computer and the printer, and producing a header page with classification level for printed documents are also viable options, but requiring a key code to be entered on the printer is the most secure.