by Mark H. Anbinder, Jeffery Battersby, Jeff Carlson, Glenn Fleishman, Kirk McElhearn, Macworld.com  

Mac users don’t need to worry about viruses.

FALSE We’ve enjoyed a long, glorious stretch without serious malware affecting our platform. But that doesn’t mean we can afford to let down our collective guard. If there is a virus attack, those of us who have good, up-to-date antivirus software installed will have the best odds of escaping unscathed.

Mandatory Measures If you don’t have antivirus software installed, see “Select Your Shield” for help. If you can’t name your antivirus program even though you’re just positive you’ve got one installed, you’re halfway there. But this is a telltale sign that you haven’t used it recently enough.

Just as important as having the software is making sure its virus definitions —the frequently updated information that antivirus software uses to recognize a virus—are recent. The best way to do this is to check for definition updates regularly. If you use a product that has an automatic update feature (all the programs described in “Select Your Shield” do), make sure it’s turned on and set to a frequent update schedule. Weekly updates should be adequate for most users, but if your computing involves accessing lots of files from lots of sources—whether via e-mail, file servers, or Web downloads—then daily updates might be a better idea.

Stay Alert Don’t open unexpected e-mail attachments until you’ve confirmed that they’re from the sender they appear to be from. Research from Sophos shows that one in 18 e-mails circulating during the month of November 2004 contained viruses.

Most malicious scripts affect only Windows machines, so if you click on one by accident, nothing will happen. But if you use Microsoft Word or Excel, you’re vulnerable to some platform-agnostic macro viruses. Protect yourself by turning on the Warn Before Opening A File That Contains Macros option in each program (under program name : Preferences: Security), but be aware that not all macros are malicious. The person who sent you the document might have included a useful macro on purpose.

To further reduce the risk of infections, don’t download free software or shareware from anywhere but reputable sources such as VersionTracker.com, MacUpdate, or the Apple software download page.—MARK H. ANBINDER

You’re vulnerable to Windows viruses if you run emulation software.

TRUE If you’re running Microsoft’s Virtual PC or another emulation product and running Windows, your Windows environment is susceptible to all the maladies that a stand-alone Windows PC is. Virtual PC and similar tools don’t merely let you access Windows-created documents and run software intended for Windows machines; you’re actually running the Windows operating system.

Virtual PC, Real Viruses You can minimize the risk by keeping your Windows environment meticulously up-to-date via Windows Update, by turning on the built-in firewall in Windows XP’s Security Center, or by installing your own firewall. (Yes, that might mean running a Mac firewall and a Windows firewall.)

Also helpful is avoiding some of the security holes that leave Windows users open to viruses and other malware. For starters, don’t use Virtual PC’s Virtual Switch network setting, which lets your virtual Windows computer act as though it were hooked directly to your network. If you put Windows right on your network with its own IP address, it’s vulnerable to any network-based attacks, such as those that exploit Windows file-sharing vulnerabilities. (Once Windows has been compromised, portions of your Mac’s hard drive that have been shared within Virtual PC might be accessible.)

Instead, use Virtual PC’s shared-networking scheme. (Select Shared Networking in the Networking tab of each virtual PC’s Settings dialog box.) This offers protection similar to that of a company firewall or a home broadband router, separating your computer from the Internet at large.

Finally, if you’re running Windows, you need antivirus software installed in Windows, not just on the Mac side. See Macworld’ s sister publication PC World for recommendations.—MARK H. ANBINDER