McColo: Are the 'Lights On" at Telia?

Chris Lewis clewis at
Sun Nov 16 05:07:34 UTC 2008

Matthew Moyle-Croft wrote:
> Is the spam SMTP meant to be originating from the McColo ranges or is it 
> being used to control other machines elsewhere?

On the spam front, it's mostly command and control connections inbound
from infected machines to McColo-based controllers.  Hence, unless you
can "watch" an infected machine in your own netblock, you don't know
that it is being controlled from McColo.

A transit provider could port block the inbound traffic, if they knew
the ports, but that would presume that the BOTs don't try to get around
that.  And we do know that some BOTs can get around that.

Secondly, from the transit provider's perspective, an outright depeer is
probably easier to defend than selective (and probably having to be
"secret") firewalling.

If they're connected again, at least some of the Botnets don't seem to
be back in full operation yet.  Ozdok/Mega-D and Rustock doesn't seem to
have started recovery (well over 95% down).  Srizbi showed some brief
renewed activity 12-24 hours ago (perhaps 10% of its former glory), but
seemingly nothing since.

> Alternatively it seems a strategic advantage for a large amount of spam 
> to originate from a single location with a small range of IP 
> addresses.   We could all just block tcp 25/465 at our borders for their 
> ranges and/or just to our mail clusters.  Although the last might leave 
> customer mail servers vunerable, but at least no one could accuse us of 
> filtering them (sore point in Oz at the moment!).

The difficulty is that local blocking is only useful to block C&C
communications from infected machine in _your_ netblock.  It doesn't at
all stop inbound port 25 connections from infected machines elsewhere.

In some limited cases, you might see a benefit to blocking DNS queries
from their netblocks.  Some "spam-by-compromised-machine" mechanisms
have the C&C doing the MX lookups for the victims.  Mostly because the
"compromised machine" is merely a proxy, and _can't_ do the MXes.  I
doubt these BOTnet C&Cs do.  More efficient to have the BOTs themselves
doing it.

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