Data communication between the clients and the server can always be intercepted. From clear text, to AMF, simple encoding, symmetric encryption, shared keys, and asymmetric encryption, they all can be seen. It is extremely hard to write a bullet-proof solution, but if you really need it, learn it here.
Questions Answered:
What is data security?
What problems could arise of unsecured communications?
I use SSL, am I safe?
How do I intercept communications, people really do that?
What is encryption?
How do different encryption methods compare to each other?
What is the overhead of data encryption?
People can always decrypt, is it worth it?
What tools are available to help me profile my application?