This is a first for the Steve Job’s Mac OS where internet security firm Intego found a Trojan malware that lures Mac users by masquerading as a codec download. A malware is not a virus, it can’t self-propagate from one machine to another.
From MacWorld: 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.
More info on how to detect and remove using the link below.