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These messages, with subjects like “UPS packet N3621583925”, purport to come from the package delivery company UPS. The message body informs the recipient that it was impossible to deliver a postal package sent by them and advises them to print out a copy of the attached invoice copy.

The invoice is included in an attached “.zip” file that contains an executable file disguised as a Microsoft Word document with names like “UPS_invoice”. However, if the targeted user runs the file, they will be introducing a copy of the Trojan into their computer.

The malicious code copies itself to the system, replacing the Userinit.exe file in the Windows operating system. This file runs the Internet Explorer browser, the system interface and other essential processes. For the computer to continue working properly and in order to avoid raising suspicion of the infection, the Trojan copies the system file to another location under the name userini.exe.

“All this effort not to be noticed is in consonance with the current malware dynamic: cyber-crooks are no longer interested in fame or notoriety; they are out to get financial returns as silently as possible”, says Luis Corrons, Technical Director of PandaLabs.

Finally, Agent.JEN connects to a Russian domain (already used by other banker Trojans) and uses it to send a request to a German domain to download a rootkit and an adware detected by PandaLabs as Rootkit/Agent.JEP and Adware/AntivirusXP2008. This increases the risk of infection even more.

“We had seen cyber-crooks use erotic pictures, Christmas or romantic cards, fake movie trailers, etc. as bait to make users run infected files. However, it is not usual to see baits like this one”, explains Corrons. “This clearly indicates that cyber-crooks are trying to use baits that do not raise suspicion to spread their creations”.