this gets covered a lot. there are some on here like rOO+ that will say that if the gov't wants you bad enough, they will get through it - which I suppose I agree with him, just not the speed at which he claims it will happen.
cryptography (the study of encryption - breaking it and making it better) is my number one hobby along with programming - there is much written about this - but yes, if you are elite to another elite account, or any other hush liscensed server, then it is secure - you have to stay in their system, otherwise it gets sent out plain text.