Fake codec trojan disables anti-virus software

Posted by   Virus Bulletin on   Aug 5, 2011

Victim tricked into believing security software still active.

A new trojan, discovered by researchers at ESET, spreads itself via fake codecs, then disables running anti-virus solutions and makes the user believe that the anti-virus is still running.

The trojan spreads via Facebook chat and engages in a short, probably automated, conversation with the victim before showing them a link that appears to contain a video of them. The link points to a fake YouTube page where user is told to install an update to Flash Player before they can view the video. This 'fake codec' trick has been used by malware authors for quite some time; in this case the attackers have added to the apparent authenticity of the link by leaving comments on the video which make it appear as if other users also had to update, but that they thought it was 'worth the effort'.

Of course, the Flash 'update' is in fact a trojan, dubbed Win32/Delf.QCZ by ESET. Upon installation, the malware detects which anti-virus solution is being used on the computer and attempts to disable it by removing its directory. To do so, it makes changes to the registry and needs to have the computer restarted in safe mode. If the user does not do so manually, a (fake) anti-virus warning pops up informing them about an 'incurable' virus which requires a reboot to be removed.

Upon de-activation of the anti-virus software, its icon is left in the system tray, thus fooling the user into believing it is still running and their computer is still protected. Clicking the icon, however, gives another fake warning that the AV software is running in 'advanced protection mode'.

Having thus disabled protection of the victim's machine, the trojan opens a backdoor which is used to install other malware onto the system.

Posted on 05 August 2011 by Virus Bulletin

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