Invisible ink was known as "sympathetic stain" during the Revolutionary War. By any name, it was an effective spying tool.

Chances are, you’ve heard of the police code 10-4, which means “affirmative” or an acknowledgment of a message. But if you hear a police officer say 10-33, there’s a police emergency underway. However ...

An anonymous bidder has won the solution to a 35-year-old puzzle for nearly $1 million. The top-secret code could be used to solve Kryptos, an infamously enigmatic sculpture containing four hidden ...