According to Symantec researchers and the company's telemetry data, the number of computers infected with the W32.Waledac.D variant is on the rise again, and most of them are concentrated in the U.S.
This latest increase can be attributed to the influence of the Virut botnet, which has apparently been hired to distribute the aforementioned Waledac botnet variant.
Waledac's goal is to send out spam emails through servers from a list that it receives from the botnet's C&C servers, and according to the researchers' estimates, that might currently mean anywhere between 1.2 billion to 3.6 billion spam emails per day.
The email subjects vary, but the links contained in them mostly lead to Canadian online pharmacies and counterfeit performance-enhancing drugs.
"The coexistence of Virut and Waledac on a single computer is further example of malware groups using affiliate programs to spread their threats, and that threats can be linked and coexist on an already compromised computer," the researchers concluded.