I actually considered this possibility many years ago. It occurred to me that on-line games and other apps could offer a means of meeting and communicating without using traditional channels. The government can tap your phone, intercept your mail and easedrop on your Email, AIM, IRC and pretty much any other recognized communication medium. Due to game design and limitations on the breadth of an allowed search via warrant monitoring in game communication can be problematic from a legal position.
I'm not necessarily agreeing with the government attempting to do so, but I do admit that what they claim is a possibility. Truth is, there are many many ways to communicate via the Internet that are extremely hard to detect.
How about this:
Step 1 - Take your message and split it into 2 parts, each part contains a nibble of each byte. That means each part contains half of each character.
Step 2 - Encode those nibbles into JPEGs, MPEGs or any number of file formats. Many formats have what amounts to "garbage areas" within them. You can pad anything you want there without affecting the operation of the file.
Step 3 - Upload to a public area, such as a binary newsgroup or perhaps a picture sharing site.
Step 4 - Receiver downloads the files and processes them to extract original message. Receiver knows what files to look for via a pre-arranged method.
If you encrypt the original message then it is much harder to detect and decipher the original message. Uploading many files with random junk data in them helps to confuse the issue. You can also break the message into more parts. I'm just giving a simplistic example here.
