I'd had one of those reality-bending moments last week that made me say, "Are you kidding me?"

A support document on Apple's Web site appeared that suggested users install anti-virus software on their Macs.

That advice countered a key marketing appeal of Mac OS X and made those of us who follow Apple wonder if something bad was coming down the road.

Currently, Mac OS X is essentially immune to the types of viruses that are so common under Windows that Microsoft has finally decided to offer anti-virus software along with Windows. I haven't recommended that Mac users run anti-virus software since well before Mac OS X appeared, because there are no credible threats.

The document turned out to be outdated; someone applied a minor edit that changed its date, leading people to believe the virus-free Mac was suddenly vulnerable. Apple quickly removed the post. I'm sure the companies that make and sell anti-virus utilities for the Mac were thrilled.

if you're really concerned, you can download ClamXav (www.clamxav.com), a free (donations accepted) virus checker based on the open-source ClamAV anti-virus software. It's designed to be run on e-mail attachments and downloaded files to ensure there isn't a malicious payload attached.

I'm sure we'll see a virus threat emerge at some point; although the architecture of Mac OS X makes it difficult to deploy a virus, it's not impossible. But instead of buying and running software that guards against nonexistent threats, you're much safer by never clicking suspicious links in e-mail (which scammers use to trick people into giving up important personal information such as credit-card numbers) and being careful about what you download from the Internet.

Connect them using an inexpensive drive connector such as the Newer Technology USB 2.0 Universal Drive Adapter (www.newertech.com). When making duplicates, I don't need a drive in an external case with its own power supply. Just dupe the drive and take the dupe to the office or to a safe-deposit box as an off-site backup. Having two duplicates, rotated a few weeks apart, reduces the chance of data loss even further.