So there has been a lot of press on the Russian spies and their use of steganography. The idea of hiding something in plain sight that only the sender and recipient know about is interesting in that it has been around as long as humans have needed to hide information from each other. The Code Book by Simon Singh is a good read for anyone that is interested in cryptography in general.
Update: Talking about cryptography being used throughout history, apparently Plato had hidden messages in his writings that were just deciphered.
