Our people screwed this basic principle up regularly with an otherwise secure product per a defector from a foreign, intelligence service: "If you have a STU-I

Our people screwed this basic principle up regularly with an otherwise secure product per a defector from a foreign, intelligence service: "If you have a STU-III secure telephone, use it, but remember that even the STU-III depends upon strict telephone security discipline. A defector from one of the foreign intelligence services that monitor U.S. communications reports that STU-III encryption is fairly secure. However, he also advised that the chitchat that occurs before the STU-III is switched to secure mode and after it is switched off of secure mode is a bonanza of valuable information. Communications monitors can identify STU-III lines, so these phone numbers are obvious targets. Therefore, a STU-III line being used in non-secure mode may be more likely to be monitored than another line that never carries encrypted communications. Maintaining strict telephone security discipline is critical." (my emphasis added) http://www.tscm.com/stu.html http://www.tscm.com/stu.html I'll also note that stopping these accidental leaks was part of the motivation for the Compartmented Mode Workstations that weren't secure enough at B1 class to stop well-funded attacks that B3 or A1 might. Risks ranged from cut/paste to classified docs making it onto unclassified networks. The systems' security kernels would look at the labels to catch that. The kinds of leaks they addressed still happen to both innocent users and criminals.