If rumours are true, then the next version of OS X - Snow Leopard - contains baked-in antivirus software. A screenshot has surfaced of a DMG downloaded by Safari being stopped in its tracks by the operating system.
The dialog box names the virus as "OSX.RSPlug.A" then prompts the user to eject the disk image. It's not clear where it's getting the virus definitions from or how often they're updated - something that's key to any effective virus prevention strategy.
Earlier in the year, Sophos warned Mac users to "be on their guard" for websites hosting malware that targets Apple computers. Traditionally, the company hasn't had a large enough marketshare to bother about malware in the same way the Windows users have to.
We'll be able to confirm or deny this report when Snow Leopard is released, on 28 August.