Ultimately every system is hackable given the time and expertise!
Your comfort zone really depends on your local security measures -
typically installation of a 'firewall' which will hide the internal
structure of your network from the world.

If you're concerned, best thing to do is hire one of the many
consultants around who will test you system by hacking it (and they WILL
succeed) and then advising on the most appropriate fixes for your
particular set of circumstances.

There have been some horrendous loopholes in commercial operating
systems discovered in the past- one potentially allowed root access to
our Unix server via ftp!

>----------
>From:  Dave Lawrence[SMTP:[log in to unmask]]
>Sent:  Tuesday, January 28, 1997 9:24
>To:    [log in to unmask]
>Subject:       Hackers in your system
>
>My chief curator is concerned about security as we venture onto the
>web.  Does anyone know if people really can access other non-posted
>information off our terminals? Can someone find the database that
>includes our inventory and "steal" info about values and storage
>locations for instance?  Can the database be corrupted?  Your help is
>appreciated.  I thought I knew about computers but this one has me
>stumped.
>