At the height of the Cold War, the CIA developed unwritten rules of engagement for their spies to use against the KGB known as The Moscow Rules.
In his book, The Master of Disguise, Tony Mendez (CIA Chief of Disguise/Technical Operations Officer) wrote, "Although no one had written them down, they were the precepts we all understood. They were dead simple and full of common sense...".
Here are the Moscow Rules are given as:
1. Assume nothing.
2. Never go against your gut
3. Everyone is potentially under opposition control.
4. Do not look back; you are never completely alone.
5. Go with the flow, blend in.
6. Vary your pattern and stay within your cover.
7. Lull them into a sense of complacency.
8. Do not harass the opposition.
9. Pick the time and place for action.
10. Keep your options open.
