This tutorial explains how to close an open DNS server and obscure which version you are running.

Open /etc/named.conf
Undernieth this:

include "/etc/rndc.key";

controls {
   inet 127.0.0.1 allow { localhost; } keys { "rndckey"; }; };

Add the following, substituting 111.222.333.444 for your servers primary IP address (if your server listens on any other addresses add those 1 per line in the acl as per the others in the list)
If you are running a DNS cluster be sure to add the IP addresses of your other DNS server into the list as well.

acl "trusted" {
   111.222.333.444;
   127.0.0.1;
};

Next Find the options container and change it so that it looks like this:

options {
   directory "/var/named";
   version "I dont think so";
   allow-recursion { trusted; };
   allow-notify { trusted; };
   allow-transfer { trusted; };
};

Restart named and you should have a closed DNS server, You can add as many ACL's as you like for the different options such as recursion, notify & transfer to give you a bit more control , this tutorial is intended only to get you started.