The next thing to take a look at is the security in your system
against attacks from local users. Did we just say local users?
Yes! Getting access to a local user account is one of the first
things that system intruders attempt while on their way to
exploiting the root account. With lax local security, they can
then "upgrade" their normal user access to root access using a
variety of bugs and poorly setup local services. If you make
sure your local security is tight, then the intruder will have
another hurdle to jump. Local users can also cause a lot of
havoc with your system even (especially) if they really are who
they say they are. Providing accounts to people you don't know
or for whom you have no contact information is a very bad idea.
You should make sure you provide user accounts with only the
minimal requirements for the task they need to do. If you
provide your son (age 10) with an account, you might want him to
only have access to a word processor or drawing program, but be
unable to delete data tha