One of Mac's biggest marketing tools is that their computers are safer than their Windows counterparts. But should Mac users still run antivirus software just as a precaution?

I ran across an article by Rich Mogull at TidBITS that answers this very question.

Here are five reasons Mr. Mogull (a Mac security expert) gives to see if you should be running Mac software or not.

1) I do not recommend desktop antivirus software for the average Mac user, but you need to take other precautions. While desktop antivirus software isn't necessary (I don't use it), make sure you use email accounts that support spam and virus filtering, such as Gmail, Yahoo Mail, or Hotmail. Spam is one of the major vectors for malicious code propagation, and gateway protection will reduce your risk should an email-driven Mac virus appear. Consider switching to the Firefox Web browser with the NoScript plugin. NoScript selectively, and non-intrusively, blocks all scripts, plugins, and other code on Web pages that could be used to attack your system during visits. I also recommend you keep your eyes open and subscribe to a news source like TidBITS so if something does change, you'll know sooner rather than later.

2) If you engage in risky online behavior, use antivirus software and definitely switch to Firefox with NoScript. Risky behavior isn't just limited to browsing Web sites you might want to avoid at work. Installing strange software from non-standard locations, failing to filter for spam, installing any random social networking plugin you find, or creeping around unusual corners of the Internet can also lead to a malicious code infection. Some other examples of risky behaviors include online gambling, hacker research, illegal file sharing (or legal file sharing on the same network that supports illegal activity), browsing media-heavy sites other than brand names like YouTube, or downloading software posted to forums or lesser-known sites. It's hard to determine exactly where to draw the line, but my general advice is if you download a lot of content, engage in clearly risky behavior, or spend a lot of time browsing fringe sites (especially forums), you should take extra precautions. If you let your children, including teenagers, use an unmonitored Mac you should also take these precautions and make sure they use a non-administrative account.

3) If you exchange large numbers of potentially risky files (especially forwarded emails with attachments that aren't otherwise scanned) with Windows users, and your email isn't scanned at your mail server, consider antivirus software for their protection. If you like to pass on every email joke and greeting card that hits your inbox, you should either change your habits or consider antivirus software so you don't spread something to your Windows-using friends. If you use an email service that includes outbound filtering, and don't exchange files other than through email, you can skip the desktop filtering.

4) If you use your Mac in an enterprise environment with antivirus policies, you still need to use antivirus software. Ideally, this should be provided by your company's IT department so it is compatible with corporate standards and centrally managed. Use of antivirus software in the corporate environment is often required for a variety of reasons, including compliance or as a response mechanism in case of an internal infection. Even though your Mac might be safer, you don't want it used to spread an infection to Windows systems or become a compliance deficiency. If you're in corporate IT, some major enterprise antivirus tools support Macs and can be deployed with policies consistent with your Windows systems. While you might have reasons for not supporting Macs in the enterprise, lack of available antivirus software isn't one of them.

5) If you run Windows on your Mac, via Boot Camp or virtualization, install Windows antivirus software. Even if you're running Mac antivirus tools, they won't help you when you're running Windows. You need to protect that partition or virtual machine just as if it were any other Windows system.

He gives a little more insight into the Mac vs. Windows debate, and I would suggest you definitely read the rest of his article.