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Re: botnets: web servers, end-systems and Vint Cerf

  • From: Rich Kulawiec
  • Date: Fri Feb 16 09:24:57 2007

On Thu, Feb 15, 2007 at 09:03:17PM -0800, Peter Moody wrote:
> Dr. Cerf wasn't speaking for Google when he said this, so I'm not sure why
> you're looking that direction for answers.  But since you ask, his data came
> from informal conversations with A/V companies and folks actually in the
> trenches of dealing with botnet ddos mitigation.  The numbers weren't taken
> from any sort of scientific study, and they were in fact mis-quoted (he said
> more like 10%-20%).

Then I think they're too small -- actually, I thought 140M was also
too small, but plausible.

A couple of years ago, I had a series of conversations with some people
who have insight into very large system populations.  The question at
hand was "how many zombie'd boxes are out there?" and was intended to
yield some concept of distributed the spam problem had become.

We kept in mind the following: (a) zombies which do nothing observable
will escape external detection (b) zombies which do things, but direct
those things against hosts that aren't paying attention, will also escape
external detection and (c) zombies which do things, and direct those
things against hosts that are paying attention, but which are sufficiently
clever about how they do it, will also escape external detection.

Everyone used their methods and reasoning.  We concurred that they were
probably on the order of ~100M zombies *just based on the spam we were
seeing*, i.e. ignoring everything else.  (As in "order of magnitude".
I thought the number was perhaps 50% low; others thought it was
perhaps 50% high.  So call it a ballpark estimate, no better.)

That was during the spring of 2005.  I can't think of anything that's
happened since then to give me the slightest reason to think the number's
gone down.  I can think of a lot of reasons to think the number's gone up.

I suggest everyone run their own experiment.  Deploy something that does
passive OS fingerprinting (e.g. OpenBSD's pf) and just look at SMTP:
then correlate (a) whether the host tried to deliver spam or not
(b) detected OS type and (c) rDNS (if any exists).  If you want to
fold in data from ssh brute-force attempts and the like, sure, go ahead.
Let it run for a month and collate results.

Alternatively, look at SYN packet rates and destination diversity for
outbound port 25 connections from those portions of your own networks
ostenibly populated with end users.  Compare to what "normal" should
look like.

I've concluded three things (by doing experiements like that).  (a) Where
there are Windows boxes, there are zombies.  "Securing Microsoft operating
systems adequately for use on the Internet" is not a solved problem in
computing.  (b) As of the moment, "the spam problem" nearly equates to "the
Microsoft insecurity problem".  (Yes, there are non-Windows spam-sending
hosts, but most of those seem to be dedicated spammer servers, quickly
identified and blacklisted, thus not a serious threat to anyone who's
using a sane combination of DNSBLs.)  (c) Amusingly, it's possible
to detect new end-user allocations and service rollouts by noting when
spam starts to arrive from them.  (e.g. the Verizon FIOS deployment, if I
may use hostnames of the form * as a guide, is going
well in NYC, Dallas, DC, Tampa, Philly, LA, Boston and Newark, but lags
behind in Seattle, Pittsburgh, Buffalo and Syracuse.)