] Hydan steganographically conceals a message into an
] application. It exploits redundancy in the i386
] instruction set by defining sets of functionally equivalent
] instructions.
] It then encodes information in machine code by
] using the appropriate instructions from each set.

While looking through the presentation list for this year's CodeCon, this program caught my interest. A nice idea and it doesn't seem to have some of the negative effects of other steganographic methods, like bloating.

Hydan: Information Hiding in Program Binaries