I’ve been using Apple computers since the 1980s, and I’ve lost track of how many I’ve owned.
(Right now I have two — an iMac desktop and a MacBook Air for travel/emergencies.)
I’m not an expert, just a (very) longtime user. And a smug one.
One thing we brag about is that viruses don’t tend to affect us.
That’s why installing anti-virus programs is not only unnecessary (most of the time), but can actually mess up your machine.
The last time I brought my (previous) iMac to the Genius Bar, complaining of slow performance, the Apple Store guys just trashed the anti-virus software and my machine was back to normal.
As far as viruses are concerned, Macs:
a) represent such small market share that malicious pranksters usually don’t bother targeting them, and
b) Apple continues to “harden” its hardware, operating system, and apps to keep invasions to a minimum.
That’s why it’s especially important for Mac users to download the very latest version of the OS X and other Apple software and apps.
(Here’s a great and very recent article about Macs and viruses that covers the special circumstances when you might want to install anti-virus software.)