From Birnam Designs Wiki

Advice on general linux administration:

http://alien.slackbook.org/dokuwiki/doku.php?id=linux:admin

Most important for me to remember is using the wheel group. In /etc/group add your username to the wheel line

wheel::10:root,alien

Also look here:

http://www.mysql-apache-php.com/ssh-attacks.htm

This page describes the wheel group method again, but also how to edit /etc/ssh/sshd_conf to deny root login.