This week’s TidBITS has an interesting and well thought-out article entitled “Should Mac Users Run Antivirus Software?” It’s a good question, and they supply a good set of answers. A bit surprisingly, the gist of the article, written by security expert Rich Mogull, is “usually, no.”

Rich makes a number of good points. He starts off by saying that he feels Mac OS X is not intrinsically more secure than the current version of Windows, but that it is much less subject to viruses nonetheless, for financial reasons. That is, it is much more economical for hackers to go after Windows due to its much larger installed base.

Rich also points out that any anti-virus software is at best 85-95% effective, so it will always miss a number of viruses anyway. It also uses a number of resources on your computer, and can slow things down quite a bit (he doesn’t point out that there are also known instances of the anti-virus software being an attack target itself).

While pointing out that things can certainly change as the Mac continues to get more popular, Rich specifically recommends anti-virus software in only a limited number of cases:

1. • If you engage in “risky behavior,” which includes not just visiting “Web sites you might want to avoid at work,” (porn!) but also “installing strange software from non-standard locations, failing to filter for spam, installing any random social networking plugin you find... online gambling, hacker research, illegal file sharing... browsing media-heavy sites other than brand names like YouTube, or downloading software posted to forums or lesser-known sites.”
   

2. • If you let children use your Mac unmonitored. You should also be sure they’re using a non-admin account.
   

3. • Exchanging a large number of files with Windows users.
   

4. • Using your Mac in an enterprise with anti-virus policies.
   

5. • Running Boot Camp or Windows virtualization software. In this case you should be sure to install Windows anti-virus software.
   

Rich does an excellent job of pointing out, near the end of the article, that things are likely to change if we’re not careful. Windows Vista is turning out to be relatively secure, so there are now two things working against the Mac from a security perspective: the Mac is getting more popular, and the installed base of Windows machines is getting harder to hack. Between these two, we all need to be more diligent about security, and we need to encourage Apple to advance some of the recent security measures it started incorporating into Leopard. Only through measures like these can we “avoid resource leaching desktop antivirus in the long term” he concludes.