Steganography is the ancient practice of stashing secret text, images, or messages inside a different text, image, or message. It dates back to as early as the fifth century BC, when Spartan King Demaratus removed the wax from a writing tablet and wrote a message hidden on the wood underneath warning of an imminent invasion by Xerxes. Steganography was a common technique used by German spies in both World Wars. More recently, it has been used to conceal highly advanced espionage malware inside image files and stash secret al-Qaeda documents inside pornographic images.
Now steganography is going mainstream with a service that embeds hidden messages inside more or less ordinary Twitter messages. Users need only type the text they want others to see in one field and the hidden message in a separate field. The service, created by New Zealand-based developer Matthew Holloway, then spits out a tweetable message that fuses the two together in a way that's not noticeable to the human eye. Take the following tweet:
— Dan Goodin (@dangoodin001) May 8, 2014