Otherwise, I agree about a wired network. 100% compatible, much faster, cannot be hacked into (well other than by GCHQ using Van Eck etc).
For true security, fibre is the way to go - no EMR to be picked up and converted back to recover the electrical signal, and can't be tapped into without being discovered (provided you are looking).
But we are venturing into the realms of the paranoid here (i.e. government).
SD