Malware + Recommended

Mac Flashback Trojan horse masquerades as Flash Player installer package – Intego Security Memo

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Malware: OSX/flashback.A

Risk: Low; this malware has been found in the wild, and may fool Mac users who don’t have Flash Player installed. However, Intego so far has only one report of this malware, and a sample provided by a user who downloaded it from a malicious web site.

Description: Intego has discovered a new Trojan horse, Flashback, which masquerades as a Flash Player installer. This Trojan horse has been found in the wild, and has some disturbing actions.

Users visiting certain malicious websites may see a link or an icon to download and install Flash Player. Since Mac OS X Lion does not include Flash Player, some users may be fooled and think this is a real installation link. When they click the link, an installation package downloads, and, if the user is using Safari as their web browser, the Mac OS X Installer will launch. (Safari considers installer packages, with .pkg or .mpkg extensions, to be “safe” files and will launch them after download, if default settings are used.)

If the user proceeds with the installation procedure, the installer for this Trojan horse will deactivate some network security software (code in this malware specifically targets and deactivates Little Snitch, but has no effect on Intego VirusBarrier X6), and, after installation, will delete the installation package itself. The malware installs a dyld (dynamic loader) library and auto-launch code, allowing it to inject code into applications the user launches. This code, installed in a file at ~/Library/Preferences/Preferences.dylib, connects to a remote server, and sends information about the infected Mac to this server: this includes the computer’s MAC address, a unique identifier. This will allow the malware to detect if a Mac is infected.

For now, Intego has analyzed this malware and its installation process. Intego’s security researchers are analyzing the injected code and we will issue more information as soon as possible.

Means of protection: Users should not download a Flash Player installer from any site other than Mac OS X Lion does not include Flash Player, but users who wish to install this software should visit Adobe’s website:

UPDATE: As of 2020, it is no longer advisable to download Flash Player, period.

Next, it is advisable, for those who use Safari as their web browser, to uncheck Open “safe” files after downloading in the program’s General preferences. This will prevent installer packages—whether real or malicious—from launching automatically.

Finally, if an installer claiming to be a Flash Player installer appears, users should be very careful to ensure that they did, indeed, download it from Adobe’s web site. If not, they should quit the installer.

VirusBarrier X6 ( protects users from this malware with malware definitions dated September 26, 2011 or later. VirusBarrier X6’s real-time scanner will detect the file when it is downloaded, and its Anti-Spyware protection will block any connections to remote servers if a user has installed the Trojan horse.

VirusBarrier Express and VirusBarrier Plus, available exclusively from the Mac App Store, detect this malware with malware definitions dated September 26, 2011 or later, but these programs do not have a real-time scanner, due to limitations imposed by the Mac App Store; users should scan their Macs after they have updated to the latest malware definitions, or manually scan any installer packages they have downloaded if they seem suspicious.

Note: if anyone who has been infected by this Trojan horse knows the URL at which they got it, can you please send an e-mail to [email protected]? Thanks.