The world’s most sophisticated Trojan uncovered

March 8, 2008 – 6:38 PM

Security experts have discovered new spambot software that installs its own anti-virus scanner to eliminate competition, alongside a number of other sophisticated features.

SecureWorks has described the Trojan, which it calls SpamThru, in detail. Others vendors have come up with different names for the software. One of the signs of its sophistication though is that few anti-virus scanners are aware of it, SecureWorks said.

“SpamThru is a money-making operation, and the author takes great care to make sure that detection by the major vendors is avoided by frequently updating the code,” said SecureWorks’ Joe Stewart in the company’s analysis.

SpamThru is a Trojan that turns a system into part of a network of bots designed to send out spam, a type of operation that’s been around for several years. While the Trojan’s network doesn’t seem especially large so far – at a couple of thousand of bots – SpamThru shows that criminals are now able to treat spam software development just like any other commercial development endeavour, Stewart said.

“The complexity and scope of the project rivals some commercial software,” he wrote. “Clearly the spammers have made quite an investment in infrastructure in order to maintain their level of income.” The company has come across previous Trojans that attempt to switch off other malware, in order to maximise system resources, but SpamThru installs a pirated version of Kaspersky AntiVirus for WinGate, customised to skip files known to be part of SpamThru itself, naturally.

“It patches the license signature check in-memory in the Kaspersky DLL in order to avoid having Kaspersky refuse to run due to an invalid or expired license,” Stewart wrote. It uses a custom peer-to-peer protocol to control communication with the network, which makes the bot network harder to kill. “Control is still maintained by a central server, but in case the control server is shut down, the spammer can update the rest of the peers with the location of a new control server, as long as he/she controls at least one peer,” Stewart wrote.

Each client has its own spam engine, creating spam from a template that’s transmitted usiung AES encryption to avoid giving access to competing spammers, SecureWorks said.

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