This is easy.. :0) ..
I blocked public access from other locations. Only connections from some IP's are allowed.
Just go to:
.. and open the following file:
.. and change this section:
Allow from all
.. to this:
Deny from all
Allow from 127.0.0.1 xxx.xxx.xxx.xxx (and further ip-blocks)
Safe your files and restart your apache webserver.
Your ISP-Config administration is now protected based on the ip from which an user connects to your site..