By Andrew Brandt
While it is far from the first Trojan ever to simply fail to execute under Windows XP, it definitely caught our eye that a variant of Trojan-Downloader-Tacticlol distributed last week in a spam campaign only fully executed under Windows Vista or newer operating systems. It may have been just a fluke, but repeated tests with both a virtual machine and real hardware running Windows XP at various patch levels showed that the Trojan we received attached to a spam message simply quit when executed in an XP environment, but ran smoothly and did all its planned dirty work on a Windows Vista testbed.
The Trojan, which is capable of causing a devastating malware infection, drops a DLL with an odd name made up of random letters into the system32 folder, then registers the DLL so it loads the next time the computer boots up. After a reboot, it kicks into full swing, pulling down a variety of malware installers.
The spam message (we got a bunch of different variations, all with the same attachment) came from a variety of falsified return addresses. The message, with a subject of Statement of fees 2009/2010 contains an utterly incomprehensible body, which reads, in part: “The accomodation is dealt with by another section and I have passed your request on to them today.” It looks very similar to a message I get from the toll road authority here in Colorado that uses electronic toll collection. The real entity emails a statement every so often with an attached PDF, though the real toll road statement doesn’t appear to come from the domains “reclusivebillionaire.com” or “reelsolutions.com.” Nice try, sparky.
More interestingly, though, is the idea that this Trojan, which is so prevalent and widely distributed, may signal the start of a trend where malware authors begin turning away from XP as the dominant operating system they target.