Currently considered unbreakable,
a code encryption technique called "steganography" is used to bury a message in
a digital image, audio, or video file. The sender uses a unique key to encode the
file and then posts it somewhere on the Internet (e-Bay, discussion group, etc.).
The receiver visits the site, downloads the file and uses a matching key to decode
the message. The boys at NSA aren't too happy about this one.