Seventh-century Persian king Khosrow II is said to have tested the loyalty of courtiers whom he believed were becoming too close. Telling one of his decision to execute the other, he would swear the man to secrecy and then watch the friend’s behavior. If it went unchanged, he knew the first man was loyal and had kept silent; if different, he was a traitor and dealt with accordingly. 

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.

Concerned about pigeons carrying military communications, German troops in occupied Belgium during World War I would shoot at overhead flocks. Such fears had not abated by World War II, when the British government ordered a systematic slaughter of pigeons throughout the UK, and inmates at British and Australian interment camps were banned from approaching birds on compound grounds.