Q. My son got a MacBook for Christmas. He seems to think that Macs are invulnerable to viruses, malware, etc. Could you do a step-by-step on securing a Mac? I know he’d listen to you.

A. Your son isn't far off. Experts put Apple's market share at 8% at the end of 2007. Microsoft's market share was 92%. That means many more people own Windows PCs than own Macs. And Windows PCs are much more likely to be attacked.

Criminals haven't spent much time attacking Macs. Mac users enjoy some immunity due to their small numbers.

That doesn't mean they are invulnerable. There have been pieces of malware written for Macs. And Mac OS X isn't impenetrable. Apple patched around 200 bugs in 2007. These covered various Apple programs, as well as security vulnerabilities.

There are some things you can do to secure your new Mac. Mac OS X comes in several flavors. I'm only going to cover the two most recent. Most people will have one of these. They are Mac OS X 10.4 (Tiger) and Mac OS X 10.5 (Leopard). Your son's MacBook is brand new. So it's probably running Leopard.

1. Turn on the firewall

Macs have a built in firewall. You should be using it. But Apple has it turned off by default. So you'll need to go in and activate it. Do this before you connect to the Internet.