By Andrew Brandt
A Trojan that pulls a sly performance of now-you-see-me-now-you-don’t disguises itself on an infected system as the Adobe Updater, a real program that’s installed alongside such mainstay applications as the Adobe Reader. This method of hiding in plain sight means the downloader, Trojan-Downloader-Karagany, may remain active on an infected system for an extended period of time, reinfecting PCs even after the more obvious payloads have been cleared up.
During the initial infection, subtlety is this Karagany’s strong suit. When executed, it pulls an act I find slightly more interesting than the conventional file copies itself from one place to another, then deletes the original behavior that is so common among contemporary malware.
In this case, the malware app (which uses an Adobe icon) does copy itself to another location — the \Application Data\Adobe folder under the currently logged-in user’s account, using the filename AdobeUpdater.exe — but leaves behind a benign program afterward, in exactly the same place as the original, and with the same filename as the original. Watch this video to see just how slick this shell game can be.
The Trojan makes a duplicate of a legitimate Windows app (the Microsoft HTML Application Host, or MSHTA.exe), naming the copy with the same filename the Trojan used at the time it was executed, and replaces itself with the renamed MSHTA.exe in precisely the same location. The effect is low-key — the program simply seems to lose its icon.