One of the three botnets cut off by the shutdown of rogue ISP McColo is back in business. The Mega-D botnet is back on its feet and throwing off huge volumes of spam, net security firm Marshal8e6 reports.
The botnet - best known for spamvertising adverts for penis pills - has been linked back to a network of compromised zombie PCs through a new command and control infrastructure. Analysis of where these systems are located is ongoing and neither Marshal8e6 or its competitors are prepared to point the finger of blame just yet. What's not in any doubt is that junk mail from compromised systems is on the rise.
"Spam from Mega-D has been ramping up over the last few days and reached up to 48 per cent of all the spam we captured in our honeypot spam traps," according to Phil Hay, lead threat analyst for the Marshal8e6 TRACElabs.
The shutdown of McColo last month was accompanied by a huge drop in the global levels of junk mail, with spam levels dropping to a third of their normal levels. Spam volumes are beginning to return to normal, according to security watchers. "Spam volumes are still only about 40 per cent of where they were in September this year but they have doubled since the last week of November, so the spammers seem to be clawing their way back,” said Hay.
Command and control servers for three botnets - Srizbi, Rustock and Mega-D - used to co-habit within McColo network. The Srizbi botnet briefly stirred last week before flat-lining again. By contrast the reanimation of Mega-D seems to be proceeding far more smoothly. Marshal8e6 reckons that the revamped botnet is a different beast using spam templates previously used only by other botnets, for example.
"The Mega-D bots appear to have been upgraded and altered quite substantially by the people behind it. It now uses templates we have seen before with Rustock," said Hay. "This could mean that the Mega-D spammers have looked at and copied from their rivals. Or, it could indicate that the individuals behind both botnets are working in collusion or are one in the same."
There's generally agreement among other security firms that junk mail levels are increasing to pre-McColo shutdown levels but some confusion about which botnets has woken up to pump out the gunk.
IBM's ISS security tools division also notes increased spam levels. It reckons junk mail volumes are half what they were immediately prior to the McColo takedown, or the same level as at the start of 2008.
The firm notes an "increase in small, HTML-based mail with minimal or no text and an embedded picture URL" that has led to a drop in the size of spam messages from 3.5k to 2.5k, on average. The slimming down in message size might have been forced on spammers by a reduction in available bandwidth, following their eviction from McColo. However it blames Srizbi, which by most accounts returned to the grave last week, rather then Mega-D for the rise.
As part of its annual report - published last week. MessageLabs ventured the opinion that of the three botnets hosted by McColo only Srizbi remains homeless.
"With the exception of Srizbi, the affected botnets have since found alternative hosting, resulting in a return to spam levels close to those before the takedowns, with rival botnets such as Cutwail and Rustock taking-up the slack left by Srizbi's absence," it said. ®