Dubbed TDL-4, is a vicious botnet made up of more than 4.5 million infected computers, is running wild, is potentially "indestructible", warns Kaspersky.
"The malware detected by Kaspersky Anti-Virus as TDSS is the most sophisticated threat today," said Sergey Golovanov and Igor Soumenkov, researchers at Kaspersky Labs.
Peer-to-peer networking techniques have been used, meaning the botnet is difficult to track. Furthermore, if its control servers were seized or shut down the group responsible could still keep it running.
Kaspersky Labs revealed that TDL is now spread by affiliates -- a network of rogue "adult content sites, bootleg websites, and video and file storage services."
Affiliate programs from these sites use a client which makes operating system checks and then downloads TDL-4 to the computer.
"Affiliates receive between $20 to $200 for every 1,000 installations of TDL, depending on the location of the victim computer," Kaspersky added.
At present, the majority of the TDL-4 botnet is on machines located in the US, with just five per cent of TDL-4 infected machines believed to be UK-based.