This is what I have never understood. Granted, my partner works in law enforcement and she says a good portion of criminals are quite dumb (willing to discuss smuggling plans in a public facebook profile, for example) but its not like creating a encrypted messaging system has a high barrier of entry. You could create such using C# Framework libraries in an afternoon! Hell, contract the work out anonymously on Elance for a $100 or so, and you'll be immune to the security services by the end of the day.
You could do pretty well just by ripping off some C# RSA example code. Find a moderately competent programmer, pay them for 2-5 hours of work...sure, why not. Just stick to the high-level APIs and you should be fine.
But realistically, nobody will be able to shut down the FOSS tools that already exist. Use Tor or VPNs if necessary in countries with internet censorship.
You would be surprised, I think. The RSA/AES stuff in C#'s System.Security.Cryptography library is pretty robust and easy to use. Copy/Pasting from MSDN will get you quite far.
