[kryps]

http://en.wikipedia.org/wiki/Steganography

[staunch]

http://en.wikipedia.org/wiki/Deniable_encryption

[zyxley]

I imagine it wouldn't be too hard to take encrypted text and transform it into something indistinguishable from the already unintelligible spam emails that pass through global networks en masse every day.

[spacemanmatt]

Some say this has already happened.