A paper by Frank Mabry, John James, and Aaron Ferguson, all from the Information Technology and Operations Center at West Point, in the latest issue of IEEE Security & Privacy.

Unicode is rapidly becoming the preferred means for representing symbols used in creating multimedia content, especially for information that's presented in multiple languages. A vulnerability in unicode leaves such content susceptible to being used for the creation of covert channel communications.

Also at IEEEXplore.

Unicode Steganographic Exploits: Maintaining Enterprise Border Security