SpamThru Trojan bundles own virus scanner

Internet miscreants have created a spam-sending Trojan that comes fitted with an anti-virus scanner. The SpamThru Trojan attempts to reserve control of compromised machines by blocking infection by other forms of malware using a pirated copy of a commercial anti-virus scanner.

Security researchers at SecureWorks reckon the sophistication of the malware rivals the complexity of commercial software, indicating that unknown malware authors have devoted considerable effort to create one of the most potent forms of malware produced to date.

Many forms of malware attempt to block access to anti-virus software updates in order to frustrate disinfection efforts. Some are even programmed to delete Windows registry keys associated with rival forms of malware. But SpamThru is reckoned to be the first form of malware that comes bundled with its own anti-virus scanning engine, in this case a pirated copy of Kaspersky AntiVirus for WinGate.

The malware takes this scanning software from a server controlled by hackers before loading it into a concealed directory on compromised machines. The malware is then programmed to prevent the security package from making proper license signature checks before downloading new signature updates.

Ten minutes later, this software is used to check for other forms of malware on compromised machines. Checks for the SpamThru Trojan itself are, of course, omitted. Other forms of malware are removed when a compromised machine is next re-started.

The sophistication of the malware extends to the command-and-control structure used to manage compromised hosts. SpamThru uses a P2P-based control system that doesn't rely on any single control server. "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 they control at least one peer," SecureWorks researchers note.

All this programming effort is being expended so SpamThru's built in junk mail-dispatching client can operate with the minimum likelihood of interruption. The spam engine is mostly being used to dispatch stock tips as part of a pump-and-dump money-making scam.

SecureWorks' comprehensive analysis of the malware can be found here. ®