Security researchers reported another threat, a spotted Mac Trojan horse in the wild that could compromise machines running Apple Inc.’s Mac OS X 10.4 or 10.5. Last week, SecureMac, a Mac-specific vendor of antivirus tools, posted an alert saying that its researchers had found a Trojan horse, dubbed “AppleScript.THT,” being distributed from a hacker-operated site where discussions of spreading the malware via iChat, Apple’s instant messaging and video chat software, were also taking place. The company classified the threat posed by the Trojan as “critical.” The malware exploits a recently publicized vulnerability in the Apple Remote Desktop Agent (ARDAgent), part of Tiger’s and Leopard’s Remote Management component. Composed as a compiled AppleScript, or in another variant, script bundled into an application, the Trojan leverages the ARDAgent bug to gain full control of the victimized Mac.