“Secretary Morrice did this day in the House, when they talked of intelligence, say that he was allowed but £700 a year,” wrote Samuel Pepys in his diary in 1668, “whereas, in Cromwell’s time, he did allow £70,000 a year for it; and was confirmed therein by Colonel Birch, who said that thereby Cromwell carried the secrets of all the princes of Europe at his girdle.”

In July 1990, one year before the collapse of the USSR, scholar Nicholas Eberstadt testified before a Senate committee about a CIA study of the Soviet economy, which showed high Soviet meat production and per-capita milk output—exceeding U.S. levels—though shortages were widely reported by tourists and Soviet citizens. “The Soviet government routinely hides many of its efforts from outside views,” Eberstadt granted. “But where, one wonders, are the hidden stockpiles and reserves of Soviet meat?”

To send a confidential note to Cyrus the Great along heavily guarded roads, sixth-century-BC Median noble Harpagus inserted a paper message into a dead hare’s belly and ordered a servant to pose as a hunter to deliver the corpse. 

Michael Hayden, former director of the CIA and NSA, claimed while discussing the NSA’s collection of telephone-call metadata, “We kill people based on metadata,” quickly qualifying, “But that’s not what we do with this metadata.” When declining an interview about alleged U.S. cyberattacks on Iran, he sent a one-line email that read, “Don’t know what I would have to say beyond what I read in the papers.”

About 40 percent of employers peer at the social-media profiles of prospective candidates, and 40 percent of party guests admit to snooping through a host’s medicine cabinet or drawers. The percent of women who admit to having looked through a partner’s phone without permission is 34 percent; of men, 62.