We typically hear about malware makers taking aim at Windows systems – which makes sense given the large install base – but with the rise in popularity of Apple and its OS X operating system, more and more we’re seeing dangerous malware, viruses and Trojans now being targeted for the Mac, too.

A new Trojan reported by SecureMac is an example of that, with the security vendor saying that variants of the AppleScript.THT Trojan horse spotted in the wild could affect users of Mac OS X Tiger and Leopard. The Trojan exploits a vulnerability within the Apple Remote Desktop Agent enabling complete access to a user’s system. It can log keystrokes, take screen shots, take pictures with the iSight camera, and enable file sharing, all while avoiding detection by opening ports in the firewall and turning off system logging.

The vulnerability is rated critical and in order to get infected a user must first download and install the malicious file, which is being distributed as both a compiled AppleScript or as an application bundle. SecureMac of course took the opportunity to pitch its MacScan antispyware security software as a solution for against this threat.