As you may have read, a new piece of OS X malware has been discovered. Intego has named this malware the OSX.RSPlug.A Trojan Horse. Note that this malware is not a virus—it can’t self-propagate from one machine to another. It is, however, definitely malicious, and it’s packaged in a well-designed trojan horse  wrapper.

According to Intego, the Trojan has been found on several pornographic Web sites. When trying to view a movie, the user is told that “Quicktime Player is unable to play movie file. Please click here to download new version of codec.”

When the user clicks the link a disk image (.dmg) is downloaded to the desktop. When the user installs the software, they are actually installing the Trojan, not a free video codec. The Trojan is installed with full root privileges, which means it has access to all files and commands on the system.

Your machine could be infected if you’ve recently gone looking for some, um, less-than-flattering pictures of Britney Spears. Thinking you’ve found what you’re looking for, you click a video to watch it, only to see a message stating that your machine lacks the necessary codec.

A disk image will then start downloading, and (depending on the settings on your machine) may then mount and launch an installer which asks for your admin password.

Intego has updated its virus definitions to remove the malicious code and prevent it from being installed.