Security researchers have decapitated a spam-spewing network of hacked computers by pulling the plug on the central command-and-control servers. The compromised PCs were infected by the Virut virus and were being remotely controlled from these servers by miscreants.
The takedown operation was coordinated by CERT Polska, the computer emergency response team in Poland. Virut - which spreads via file-sharing networks, compromised web servers and infected USB drives - was responsible for 6.8 per cent of malware infections in 2012, according to stats from Russian security biz Kaspersky Lab.
The software nasty infects .exe and .html files to display adverts and open a backdoor to the botnet's masters. It has been linked to data theft and distributed-denial-of-service attacks, as well as spam distribution, according to CERT Polska. Other researchers, including the bods at Symantec, have linked the botnet to ad-click fraud.
“Since 2006, Virut has been one of the most disturbing threats active on the Internet,” CERT Polska wrote. “The scale of the phenomenon was massive: in 2012 for Poland alone, over 890,000 unique IP addresses were reported to be infected by Virut.”
CERT Polska has sinkholded 23 domain names, including zief.pl and ircgalaxy.pl, used by servers calling the shots not only for Virut-infected machines but also systems hit by the Palevo strain of malware and variants of the infamous bank-account-raiding ZeuS Trojans. Sinkholing involves seizing control of the domain names for a botnet's command-and-control systems to redirect connections from the hacked PCs to investigators' machines.
This allows the security experts to capture communications from compromised computers phoning home to the command-and-control servers to receive their next instructions. This reveals the operations and internal structure of the network of zombie PCs, which steers the strategy for subsequent cleanup operations. Seizing the reins of the botnet to monitor network chatter disrupts the criminal activity, at least temporarily, but in itself does nothing to remove infections from compromised drones - which are, don't forget, innocent users' Windows PCs.
As a back-up mechanism each compromised Virut host can try using one of 10,000 alternative domain names each day to connect to a command server if contact with the main control systems is lost; this feature allows the zombie masters to rollout fresh updates and new connection details and regain control of the botnet. Days before the takedown, Symantec warned that Virut was redistributing Waledac, a spam-sending bot whose original control system was pulled offline in a high-profile takedown operation orchestrated by Microsoft in 2010.
The Virut botnet created a platform for the distribution of other strains of malware onto compromised hosts and this formed the main mechanism for its controllers to make money, often through elaborate affiliate programs.
One money-making affiliate network aped legit software businesses by actually publishing an end-user licence (EULA) for Virut, according to investigative journalist Brian Krebs. The terms-of-use document, for those wishing to redistribute the virus, refers to "bundling" rather than infection, and boasts that "QuickBundle technology" spread by the botnet "enriches" files with ad-supported content.
The licence forbids users from sharing the download with computer security organisations or anti-malware firms. ®
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