Loading external assets from Server

Hello,
I’m creating a MMO Game using SmartFox Server + MySQL + memcached
in the game world there is planty of objects and clothes for the characters.
ofcourse all those objects should be on the server, and the client load them dynamically (the assets = swf files)

there is no doubt about the above-mentioned thought, but my question is about the implementation. I guess it should be an HTTP server (Apache/Jetty etc…)
and the clients gets a list of URLs. is it right?
what security issues should I pay attention to? for example, I don’t want that everyone will have the ability to download my assets and steal my graphics.

I will appricate your help
thanks alot (and in advanced)

flash2070