There’s a new piece of malware out there targeting Mac users that takes advantage of the inclination to watch porn.

Dubbed OSX.RSPlug.A by its discoverer, Mac security vendor Intego, the Trojan is being downloaded by users responding to spammed forum postings promising free porn.

When they follow the links in the messages, they are told that QuickTime cannot play the movie file and are presented with a link to what is claimed to be a new codec. If the code is downloaded and installed, it asks for an administrator password and then changes the Mac’s DNS settings to point to a server presumably operated by the miscreants behind the Trojan.

If you’re running Tiger, you might never realize how you were infected, but Leopard’s Advanced Network preferences will at least let you recognize that the DNS servers have been changed. You’ll be unable to change them back without going through a lengthy process detailed by Macworld’s Rob Griffiths.