The bug is spread via the built-in iChat instant-messaging program and infects computers when users download a file called "latestpics.tgz:" and install it on their machines.
Apple released a statement on Thursday advising Mac users to "accept files from vendors and Web sites that they know and trust."
CBS News technology analyst Larry Magid explains that viruses and worms that target Macs are "extremely rare but not unheard of."
"It's not that Mac is inherently virus-proof; it's just that there are so few of them that it's not that attractive a target," Magid explains. Any device that can be programmed, from computers to cell phones to personal digital assistants (PDAs), "can be hacked or attacked," Magid says.
In light of the Mac worm news, a Sophos Web poll found that 79 percent of those surveyed believe that Macs will be targeted more in the future. However, more than 50 percent of those polled said they don't think the problem will be as great for Macs as it will be Windows.