In a Securelist blog, Kaspersky researchers Sergey Golovanov and Igor Soumenkov outlined a new evolution of the TDSS bot, which they describe as "the most sophisticated threat today."
"The owners of TDL are essentially trying to create an 'indestructible' botnet that is protected against attacks, competitors, and antivirus companies," the researchers say.
"The way in which the new version of TDL works hasn’t changed so much as how it is spread -- via affiliates," the blog states. "As before, affiliate programs offer a TDL distribution client that checks the version of the operating system on a victim machine 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," the researchers explain. "Affiliates can use any installation method they choose. Most often, TDL is planted on adult content sites, bootleg websites, and video and file storage services.
"The changes in TDL-4 affected practically all components of the malware and its activity on the Web to some extent," the blog states. "The malware writers extended the program functionality, changed the algorithm used to encrypt the communication protocol between bots and the botnet command and control servers, and attempted to ensure they had access to infected computers even in cases where the botnet control centers are shut down."
Many researchers say the changes to the TDL rootkit are impressive, but some doubt the suggestion that it might be indestructible.
"As a 24-year veteran of the malware wars, I can safely tell you that no threat has appeared that the antimalware industry and OS vendors did not successfully respond to," said security expert Roger Grimes in his blog. "It may take months or years to kill off something, but eventually the good guys get it right."
"It's not new for malware to delete other malware on a system," says Jack Walsh, network IPS program manager at ICSA Labs, which does security product certification and testing. "That's been done before. In the past, it was more done to spite the other malware writers. Nowadays the reasons are more evolved.
"Once a PC becomes part of the TDL-4 botnet, those managing the army of bots don't want to share the infected PC with others botnets," Walsh observes. "The malware removes competing malware because of money: Eliminating its botnet competitors makes this TDL-4 malware more attractive to cybercriminals looking for malware to use that will help them make a buck."
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