The value of entity hiding

Hi All,
The NAT protocol is said to hide the NATed entities from being directly 
approached from the internet side.
To what extent does this feature count as a value, providing real security?
In spite of the entity may be really hidden but that could never protect 
against an attack in which the attacker could perform (trial and error) 
untill he discloses that there is some machine residing at the address: 
(internal one of course) 10.2.1.1 behind a NAT router: 216.235.22.2., and 
then begin to attack. So when we talk about that NAT has provided (entity 
hiding), we can consider protection as no more than a passive one that can 
never be there alone without an actual protection. Is that understanding 
right?
Mohammad Awad





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