Hi Jason, thanks a lot for your reply.
I agree 100% with your post.
I would like to have a fixed user base, XMPP server isolated from the others and the XMPP server only respond to that users requests, without advertising any capabilities or answer to any other requests other than the minimum needed...
It seems that a generic XMPP server like Openfire is not compatible with my scenario and maybe a stripped-down alternative version is needed...
I take you answer as correct, however if there is any possible configuration that can help to harden a little bit Openfire against port scanning (without change Openfire code / recompile), i would be more than happy to know.