Re: [Asrg] Countering Botnets to Reduce Spam

Rich Kulawiec <rsk@gsp.org> Fri, 14 December 2012 17:45 UTC

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Date: Fri, 14 Dec 2012 12:44:57 -0500
From: Rich Kulawiec <rsk@gsp.org>
To: Anti-Spam Research Group - IRTF <asrg@irtf.org>
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Subject: Re: [Asrg] Countering Botnets to Reduce Spam
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On Fri, Dec 14, 2012 at 10:08:48AM -0500, Chris Lewis wrote:
> Compromised Linux machines (mostly servers) are now responsible for ~40%
> of all spam.
> 
> The actual _count_ of compromised Linux machines is indeed quite low.
> Say 62K out of 8.6M observed compromised machines.  About .72%. Two 9's ;-)

I believe you.  This suggests two possibilities:

1. Somethings's broken somewhere in my experimental design between data
acquisition and statistical analysis.

or

2. We're talking apples and oranges and that's why our numbers are so
different.  To clarify: I'm not trying to measure spam volume, just
the number of systems (and their OS types).  And to clarify further:
I classify a system as a bot if it meets a set of criteria that includes
more than sending spam: I may also classify it as a bot if it's doing
brute-force SSH/FTP/IMAP/etc. attacks, if it's doing port scans, etc.
(The "may" is there because some systems engaged in these activities don't
appear to be bots.  Of course that's a judgment call and I'm sure I make
FP and FN mistakes.)

For example, if 190.147.78.102 (Static-IP-cr19014778102.cable.net.co,
thus probably in Colombia) makes 133 different IMAP login attempts,
I'm going to conclude that it's not a bored user in Bogota with
nothing better to do, it's most likely a bot doing that.

Do you think #2 explains the difference in our numbers, or do I have
to make a LOT of coffee and dig into #1?

---rsk