Given this evidence, should I be worried that I may have been hacked

[Paul Schmehl]

--On April 14, 2007 7:25:46 AM -0400 Jim Stapleton 
<stapleton.41 at gmail.com> wrote:

> Once I opened up SSH to the outside world, my machine has been
> hammered once or twice a day most days, with username failures. None
> of the  usernames would fit a username on my system (except root), and
> I have ssh set to deny root logins, and only use SSH2. Additionally, I
> have the following in my login.access (only active entry, the name
> have been changed on this, but the three names would appear as 3 and
> four character random alphabetical strings):
> -:ALL EXCEPT wrbc crr aqp:ALL EXCEPT local
>
> As of the 9th, I've only seen one set of blatant/brute-force attempt
> at my ssh server. It's interesting, but the major drop in attempts has
> me more worried than the attempts (could this drop off be because they
>  no longer need to hack me? Could they have hacked me an that be the
> reason why?)
>
> How worried should I be, and what's the best recourse for this?
>
I have a *lot* of experience with hacked boxes.  They all share at least 
one of three things in common:

1) Not patched up to date
2) Incorrectly (or not at all) configured
3) Weak or default passwords

Those three things are the cause of almost every breakin I've seen.  The 
first is by far the greatest reason for breakins.  The second and third 
are less frequently but still often the case.  It is not at all uncommon 
to find a box running unpatched and unconfigured services that its owner 
had no idea were running.

If you have any of the above conditions, then you have something to be 
concerned about.  If you don't, then the reduction in attacks is most 
likely pure coincidence.

If you don't want your computer broken into:

1) Keep it patched and up to date at *all* times.  Eternal vigilance is 
the watchword.
2) Disable *and* remove all services you do not intend to run.  Don't 
install a program if you aren't going to be using it.
3) If you want to play around with something, configure it to respond to 
localhost *only* or restrict access to known IP addresses.
4) *Always* change default passwords and *never* use weak passwords.  A 
weak password is defined as a password that does not use special 
characters.  Period.  Alphanumeric passwords can resist brute force 
attacks for approximately one week using modern computers.

Paul Schmehl (pauls at utdallas.edu)
Senior Information Security Analyst
The University of Texas at Dallas
http://www.utdallas.edu/ir/security/