A recent upsurge in Storm Worm activity was accompanied by a spike in spam levels 48 hours later, according to an analysis by managed security services firm MessageLabs.
After the August 15 outburst, which involved the distribution of 600,000 Trojans in only 24 hours, junk levels increased on August 17 by more than 30 per cent. These levels sustained for the next week and then returned to normal.
The August outbreak involved virtual postcards and YouTube video invites. More recently Storm Worm-themed emails have posed as links to National Football League fixtures lists.
Although the body text and subject line keep changing, the emails always consist of simple text or HTML including a single link to an IP address. That IP address refers to another infected machine within the botnet, which subsequently redirects to a back-end server in an attempt to infect the victim with a copy of the Storm Worm Trojan code. The back-end server automatically re-encodes the malware every thirty minutes to make signature detection difficult for traditional anti-virus vendors.
Infection turns PCs into zombie spam drones under the control of hackers. MessageLabs reckons the Storm Worm botnet accounts for 1.8m compromised PCs worldwide.
The location of the command and control servers used to manipulate the botnet are safeguarded behind a rapidly-changing DNS technique known as ‘fast-flux’, making it difficult to locate and take down hosting sites and mail servers.
Based on the tactics and techniques used in outbreaks, MessageLabs reckons the Storm Worm gang is a small group of young adults, likely to be in their early 20s, and from Russia.
"It is unlikely that the Storm Worm gang is an organised criminal group as the underworld, or shadow economy, is largely constructed of a loose affiliation of disconnected but highly-specialised individuals and small groups," said Paul Wood, MessageLabs security analyst. "Their motive is to make as much money from the botnet as possible."
"StormWorm’s closest rival botnet, Warezov, is likely to be Asian in origin," he added. ®