Twitter offers a surprising freedom of expression within 140 characters, but what if you want to hide a message in plain sight — say, to get around censorship? Well, it’s now as easy as pie. Matthew Holloway has built a web tool that uses steganography yo put secret phrases inside your tweets. The technique replaces letters with similar-looking characters that hide a second message you can only reveal with the right decoder.
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.