Many of the domain names used by a cybercriminal gang to control computers infected with the Virut malware were disabled last week in a coordinated takedown effort, Spamhaus, an organisation dedicated to fighting spam, announced Saturday.
The Virut malware spreads by inserting malicious code into clean executable files and by copying itself to fixed, attached and shared network drives. Some variants also infects HTML, ASP and PHP files with rogue code that distributes the threat.
Once installed on a computer, the Virut malware connects to an Internet Relay Chat (IRC) server using an encrypted connection and awaits for instructions. This allows attackers to control Virut infected computers as a botnet.
Virut is primarily used as a malware distribution platform -- other cybercriminals pay the Virut botmasters to deploy their own malware on the already compromised computers.
In the past, Virut has been used to distribute the ZeuS banking malware and the Kehlios spambot. However, last week, security researchers from Symantec warned that Virut started distributing the Waledac malware, potentially leading to the resurrection of the Waledac botnet that was originally shut down by Microsoft in 2010.
The Virut botnet masters are using several dozen domain names in the .pl (Poland), .ru (Russia) and .at (Austria) top-level domains as part of their command and control (C&C) infrastructure, Spamhaus team member Thomas Morrison said Saturday in an announcement on the organisation's website.
Spamhaus collaborated with the Polish Computer Emergency Response Team (CERT.pl) and the home.pl domain registrar to ensure that no traffic was received by the .pl domains used by the Virut botnet, a process known as sinkholing, Morrison said.
"A number of domains in .pl, most notably zief.pl and ircgalaxy.pl, have been used to host Virut, its command & control IRC servers, as well as to host other malware including Palevo and Zeus," CERT Poland said Friday on its website. "NASK, the operator of the Polish domain registry, took over 23 of these domains yesterday (Jan 17, 2013) in an effort to protect Internet users from Virut-related threats. Name servers for those domains were changed to sinkhole.cert.pl, controlled by CERT Polska [CERT Poland] -- an incident response team operated by NASK."
Spamhaus also worked with Group-IB, a Russian information security and computer forensics company, which was able to get the .ru domains used by Virut shut down in a matter of hours.
Although currently crippled, the Virut C&C infrastructure is not completely out of the hands of attackers. Their last remaining strongholds are the remaining .at domain names, Morrison said.
Spamhaus alerted the .at domain registry and the Austrian CERT multiple times about this issue and hopes that they will follow the example of their Polish and Russian counterparts in suspending the C&C domain names.
"The Virut takedown effort clearly illustrates the important and meaningful role [domain] registries and registrars can play in the fight against cybercrime in general," Morrison said. Such organisations should be proactive and add clauses in their contracts that will allow them to quickly take action against domain names used for malicious purposes, he said.
Based on information gathered during a recent sinkholing operation, Symantec estimates the size of the Virut botnet at over 300,000 infected computers.