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 ...

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 ...

Click to share on Facebook (Opens in new window) Facebook Click to share on X (Opens in new window) X Hillhouse students at work writing invisible ink messages ...

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 ...

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 ...

ALBUQUERQUE, N.M. (WHAT THE TECH?) — Like cyber criminals with AI, parents might be interested to know that people have been using invisible commands for years on apps we all use. When some of us were ...

A Hillhouse student’s eyes widened as he applied grape juice and heat to what appeared to be a blank piece of paper — but instead held a secret message in invisible ink, written as part of a course ...

SHREVEPORT, La. — 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.