Security Experts:

Virut Botnet Joins Forces With Waledac Malware

Like a bad horror movie, in the world of malware, dead doesn't always mean dead.

According to researchers at Symantec, the Waledac malware has been spotted being distributed by the Virut botnet. In 2010, Microsoft won a legal battle to takedown the Waledac botnet, which at the time was spamming out as many of 1.5 billion emails a day. Last year, researchers at Palo Alto Networks uncovered a new variant of the Waledac malware that was not only sending spam but also stealing passwords and other information.

Now, Symantec said, Virut is downloading a variant of Waledac, marking another example of how malware groups using affiliate programs to spread their wares and how multiple threats can coexist on the same computer.

"While Waledac the botnet may be dead, the malware that was distributed by it has re-emerged and has been updated," said Satnam Narang, security response manager at Symantec. "For instance, somewhat recently updated variants have the capability to steal Bitcoin wallets."

Once the computer is compromised, it sends spam emails through servers from a list that it receives from the command servers, according to Symantec. During its analysis, researchers observed a compromised computer sending roughly 2,000 emails per hour.

"Conservatively, if a quarter of the estimated 308,000 computers infected with W32.Virut download W32.Waledac.D, then potentially billions of spam emails can be sent from these computers," Symantec's Security Response Team noted in a blog post. "The following table contains some basic calculations on the estimated volume of emails from this campaign with totals ranging from 1.2 billion to 3.6 billion spam emails per day."

According to Symantec, the emails used one of sixteen unique subject lines and one of thirteen unique email message bodies. Many of the emails led to Canadian online pharmacy spam, while others led to fake performance-enhancing drugs.

"Despite the botnet being taken down, the malware persists," said Narang. "Today, it's being distributed by Virut. Tomorrow? Perhaps another botnet. Cyber criminals don't necessarily have to build a botnet when an online underground economy exists where affiliate programs and pay-per-install schemes are readily accessible."