Here we use the tools in the BackTrack 5 r3.
nmap -sS -sV -v -Pn samiux.com
perl fierce.pl -dns samiux.com
*** where "samiux.com" is the domain name, here is only an example.
From the last output result, make sure your server IP address is not listed when she says that she is hidden.
Now, your server IP address is not shown. So, your server is really hidden? I guess not, maybe. To further test it with the searchdns.netcracft.net for the history records. You may find your server's IP address history records unfortunately (if any).
If your server IP address is in the history record of netcracft, you may consider to change the IP address when necessary in order to hide your server from the internet.
That's all! See you.