Mac OS X backdoor Trojan, now in beta?


OSX/MusMinim-A screenshotIt appears there is a new backdoor Trojan in town and it targets users of Mac OS X. As even the malware itself admits, it is not yet finished, but it could be indicative of more underground programmers taking note of Apple’s increasing market share.

SophosLabs analyzed the sample we received and determined that it is a variant of a well-known Remote Access Trojan (RAT) for Windows known as darkComet.

The author of the Trojan refers to it as the ‘BlackHole RAT’, as you can see from the screenshots, but Sophos calls it OSX/MusMinim-A, or ‘MusMinim’ for short.

Note: The author of DarkComet RAT has contacted Naked Security denying this relationship, admitting his own OS X RAT is in development.

The name ‘Black Hole’ is already used by a legitimate application which actually aims to increase security on your Mac by helping you get rid of potentially sensitive information such as recently-used file lists, data left in the clipboard, and more.

MusMinim is very basic and there appears to be a mix of German and English in the user interface. Its functions include:

* Placing text files on the desktop
* Sending a restart, shutdown or sleep command
* Running arbitrary shell commands
* Placing a full screen window with a message that only allows you to click reboot
* Sending URLs to the client to open a website
* Popping up a fake “Administrator Password” window to phish the target

Screenshot of fake Admin credentials dialog

Here is an excerpt from the default text that is displayed in the full screen window with the reboot button:

"I am a Trojan Horse, so i have infected your Mac Computer. I know, most people think Macs can't be infected, but look, you ARE Infected!
I have full controll over your Computer and i can do everything I want, and you can do nothing to prevent it.
So, Im a very new Virus, under Development, so there will be much more functions when im finished."

SophosLabs has published protection for our customers as OSX/MusMinim-A. Trojans like this are frequently distributed through pirated software downloads, torrent sites, or anywhere you may download an application expecting to need to install it.

It could also be dropped by a vulnerability in your browser, plugins and other applications. Patching is an important part of protection on all platforms.

Fortunately our products can detect and remove Trojans like this, and for home use they’re free! If you would like to install Sophos Anti-Virus for Mac Home Edition, click on the banner below.

DownloadFree Anti-Virus for Mac
Download Sophos Anti-Virus for Mac Home Edition

Below you’ll see a slideshow of the Trojan in action:

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I would like to thank Mike Shannon at SophosLabs Canada for help analyzing this threat, and Meths at

Note: Blackhole RAT is not in any way related to the Black Hole software on