The 20th century counterattack on letterlocking: The CIA Flaps and Seals Manual to covertly open your mail. https://www.scribd.com/doc/59705644/CIA-Flaps-and-S

The 20th century counterattack on letterlocking: The CIA Flaps and Seals Manual to covertly open your mail. https://www.scribd.com/doc/59705644/CIA-Flaps-and-Seals-Manual https://www.scribd.com/doc/59705644/CIA-Flaps-and-Seals-Manu... The book is from Paladin Press, a 1970s-era publisher of "hard to find" information, and I don't see any evidence that it came from the CIA. But the same or better techniques would certainly have been used by spies, government agencies, and postal inspectors at the time. It's funny to think about the hard work that governments had to do back then to target an individual and read his or her mail. And people would have been outraged if they discovered that their mail had been read. How times and attitudes change.