RE: Linux hacked

Unless the system is required to be on the net while it is being rebuilt
do not connect the CAT-5 to anything that has connection to the
Internet.  As well to rebuild the system do you have the kick-start file
in / or /root?  That is if the version of Linux you are installing
supports that?  Make a rebuild a snap! now are you doing this as a
download install rather than from a CD? DANGER! Will Robinson Danger. 
;)

for relatively good security:

1) You can do yourself.
You could always set a iptables rule to drop all incoming packets.
Do you have an extra system laying around?

2) rely on another product
http://www.smoothwall.org 
http://www.ipcops.net

plus the other firewalls out there that required a dedicated machine to
install them on.

3)  BEST SECURITY
If you want 100% security make sure that the system is locked in a room
that only you have access to and that there are NO outside connections
via Ethernet, fiber optic, wireless, or telekinesis as well as any other
known or unknown methods to that system.  Furthermore you must develop
your own code and you must be sure that you know how to program in a
secure manner.  :/
Then when using this case market your product! But if you decide to be
realistic and cool like the Linux world make it open source.

:>>>

Bottom line if it is connected to the Internet, and actually allows any
communication in or out, it will eventually be compromised given
somebody has enough time or interest in trying to break your system. 

--
Leif Ericksen