1. Login to shell as root and go to the /etc directory
# cd /etc
2. View the contents of this directory.
# ls -a
3. You should have two files, one named hosts.allow and the other hosts.deny. Open the hosts.deny file using your favorite editor (I prefer vi).
# vi hosts.deny
4. On a new line, put ALL:ALL. This will disable all access to your system, best form of defense. Save the file and exist (for more information on how to us vi, type 'man vi' at the command prompt).
5. To allow certain users access, edit the hosts.allow file by adding the user's IP address.
For more information go to: http://linux.about.com/od/commands/l...l5_hostsde.htm