William Abel, a mail censor at Iowa's State Prison, Fort Madison, using a hot iron to bring out a secret message written in lemon juice on a letter.Three Lions/Getty Images Humans have had a long ...

The arrests of ten people accused of working in the U.S. as Russian spies came after an investigation that dated back to the Clinton administration. Years of video and audio surveillance and secret ...

For a long time, seeing those words pop up onscreen was the best indicator of good gossip to come. Close seconds included “OK, so…” for the more demure among us, or a simple teacup emoji for the ...

Putting secrets in texts is risky business. An email is almost certainly a no-go, as is a traditional SMS. Encrypted texting, like iMessage, is better, since only your device and the recipient’s can ...

Which invisible ink pens are best? Spies and conspirators have used invisible inks for millennia to send messages. In the modern age, invisible ink pens are an excellent way for grown-ups to ...

A ninja history student in Japan sent her education into stealth mode when she turned in a seemingly blank paper for her term essay. Eimi Haga wrote the essay with invisible ink. Haga told the BBC ...

When we were kids, “invisible ink” meant lemon juice on notebook paper, write the message, and to see it someone would have to hold it up to the light for the words to appear. Otherwise, it just ...