Online security firm Sophos reported on the virus, which operates under the name OSX/Jahlav-C.
The virus targets adult websites, quietly waiting for surfers, whom the virus then tells that they're missing a crucial video component, in this case a "Video ActiveX Object." The virus presents users with a popup window that instructs them to download the relevant file.
The virus gained some extra attention from security firms because of its adaptability. Before prompting the user, the virus determines whether they're surfing on a Windows or a Mac OS system.
Because of Mac's far smaller share of the personal computing marketplace, conventional wisdom has long held that nefarious programmers just don't build viruses for them. Sophos Senior Technology Consultant Graham Cluley said that myth has long since been disproved.
"Although there is much less malware for Mac OS X than there is for Windows, that's going to be little consolation if your shiny new MacBook gets infected," he said. "Many in the Mac community have had their heads buried in the sand for too long about the real nature of the threat."
Despite Apple's smaller market share, it has been growing, and the increasingly popularity of devices like the iPhone and iPod present intriguing possibilities for virus developers. In 2007, a Mac-specific virus emerged, and over the last year, viruses targeting YouTube and the Firefox web browser have also appeared. The YouTube virus didn't present much of a problem for Mac users, but the Firefox virus simply phished for sensitive information — and those kinds of tactics work on any operating system.