The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming. (Donald Knuth)
We often have systems that have run for years with no connection to
the outside world, and now suddenly an Internet connection is added
and ssh access is set up. Unfortunately, many users have weak or
even blank passwords.
If only some users need to use ssh, it's best to set up new
users with strong passwords and restrict ssh to only those
You do this by adding a line like this to
AllowUsers doug essex
Restart sshd after making this change (you can even do that if
you are currently logged in over ssh). Only those users will be
allowd ssh access.
Dave DiPietro noted: SCO versions may put the sshd configuration
file at /usr/local/etc/sshd_config.