The last thing you want to do is run a professional webhosting service
with outdated software that is exploitable. With Debian you can use
apt-get to download the latest packages for everything on your system.
With RedHat you can use up2date from the commandline. The bigger
distributions make this easy on you. Also, you don't want to run any
software that is so new that it hasn't been time-tested and proven to
be secure. I usually give packages a couple of months before I'm willing
to upgrade unless of course they fix a known vulnerability in what I'm
currently using.
Keep your kernel up to date also and patch it with the GRSecurity patch
to add increased protection. For information on how to patch your kernel
go to http://www.tldp.org/HOWTO/Kernel-HOWTO-7.html I recommend you read
the entire section on the kernel. If you jack up something here then
your system will basically be unusable or unstable at best.
LIMITING ACCESS TO SERVICES
First you will want to disable any unneeded services. cd /etc/xinetd.d/
and for any services that you dont want enabled change it so say
disable = yes. Once you have made all of the changes you need to restart
xinetd by issuing the command 'killall -HUP xinetd' Some other directives
you may want to use include the following which will make it harder for
your system to get bogged down or abused.
.... continued
http://www.sekure.us/sekure.html
Edit: P.S. Check the link at the bottom of the page of the link it will take you to a great reference sheet about security in PDF format




