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AppleScript.THT Trojan Horse – Mac OS X

Posted on June 7, 2008

New OS X Trojan Horse in the WildSecureMac Security Advisory

Security Risk: Critical

SecureMac has discovered multiple variants of a new Trojan horse in the wild that affects Mac OS X 10.4 and 10.5. The Trojan horse is currently being distributed from a hacker website, where discussion has taken place on distributing the Trojan horse through iChat and Limewire. The source code for the Trojan horse has been distributed, indicating an increased probability of future variants of the Trojan horse.

The Trojan horse runs hidden on the system, and allows a malicious user complete remote access to the system, can transmit system and user passwords, and can avoid detection by opening ports in the firewall and turning off system logging. Additionally, the AppleScript.THT Trojan horse can log keystrokes, take pictures with the built-in Apple iSight camera, take screenshots, and turn on file sharing. The Trojan horse exploits a recently discovered vulnerability with the Apple Remote Desktop Agent, which allows it to run as root.

The Trojan is distributed as either a compiled AppleScript, called ASthtv05 (60 KB in size), or as an application bundle called AStht_v06 (3.1 MB in size). The user must download and open the Trojan horse in order to become infected. Once the Trojan horse is running, it will move itself into the /Library/Caches/ folder, and add itself to the System Login Items.

Once installed, the Trojan horse turns on File Sharing, Web Sharing, and Remote Login. If the filename of the Trojan horse has not been changed, it can be located in the /Library/Caches folder under the name

Until a patch is issued for the Apple Remote Desktop Agent exploit, SecureMac classifies the security risk presented by this Trojan horse as high.


To protect your system against this threat, run MacScan 2.5.2 (MacScan is a product of SecureMac) with the latest Spyware Definitions update (2008011), dated June 19th, 2008. SecureMac recommends that users download files only from trusted sources and sites.

Additional removal instructions and resources will be posted once available.


WashingtonPost analysis on AppleScript.THT Trojan Horse

About MacScan:

MacScan quickly detects, isolates and removes spyware from Macintosh computers using both real-time spyware definition updating and unique detection methods.  The software also manages internet-related clutter on your computer. It is designed for Mac OS X version 10.2.4 and later, and is compatible with OS X 10.5 (Leopard). For more information, or to download a demo version of MacScan, visit

About SecureMac:

Since 1999, has been at the forefront of Macintosh system security. The site not only features complete Macintosh Anti-Spyware and Antivirus solutions, but also operates as a clearinghouse for news, reviews and discussion of Apple computer security issues. Users from novice to the most advanced will find useful information at SecureMac that is designed to make their computer experience trouble free.

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