Sophos released free personal anti-virus software for Apple Macintosh OSX last week. According to their website:
"As Apple computers grow more popular than ever, they're an increasingly-enticing target for hackers. And these hackers aren't just mischief-makers—by targeting your computer or applications you use, these criminals are out to steal and profit from your valuable personal information. Don't let them. Get free Sophos Anti-Virus for Mac today."
I highly recommend that Mac users start to look into anti-virus for their systems. There are other solutions out there. Make sure to peruse the resources section under Software and Links of this website to look at other alternatives.