It's pretty simple to secure a bind DNS server.

You should insert few lines in the bind maned.conf file.
Open the file and find the options section. Inside the options section you need to put the following 4 lines:
version none;
fetch-glue no;
recursion no;
allow-transfer { none; };

Now close the file and restart the bind. Check on the /var/log/messages log just to make sure everything started and working properly and than you shouldn't worry about it.