1. If you have a Windows computer, you must obtain and install all of the following: a reputable antivirus program, a software firewall, a junk-mail filter and an antispyware program. Even if you own a Macintosh (Macs have been unaffected by most of these threats to date), you will still need to turn on your computer’s firewall and employ a junk-mail filter.

2. Upgrade to the latest versions of the leading Windows web browsers, Microsoft’s Internet Explorer 7 and Mozilla’s Firefox 2.0, both of which warn you when a web page you’re visiting appears to be phony. (The new Internet Explorer also has under-the-hood security improvements that close some of the holes plaguing older versions.) You might also consider add-on software, like McAfee’s SiteAdvisor or the new Norton Confidential, which warn about fraudulent sites and, in the case of Norton, also about malicious software on your PC. On a Mac, consider using Firefox 2.0 instead of Apple’s Safari, which, while very good and generally secure, lacks a fake-web-site detector.

3. Never respond to or click a link within any unsolicited email message from a financial institution — even your own — no matter how official it looks. Crooks have become skilled at mimicking logos and typefaces used by banks, brokers and payment services like PayPal. When you click on links within these fake emails, you’ll be taken to web pages that look like the companies’ official sites, even down to the address, but they’ll steal your log-in information. Be especially wary of email from a financial institution that asks for account information or says you must log in at a linked site to address a problem. You can phone the company to see if there really is an issue. Obviously, this caution doesn’t apply to some financial emails, such as confirmations of online stock trades you’ve just executed. But in general, you shouldn’t conduct financial transactions via email or links in email. Instead, go directly to the financial sites you use.

4. Similarly, never act on emails offering stock tips, miracle pills or the chance to earn money by storing millions from overseas in your bank account. Sounds obvious, but in the past these scams might have cost you a little money. Now they may be part of more-damaging identity-theft schemes. Treat such come-ons the way you’d treat a stranger in a bad neighborhood who made such promises.

5. Never, ever download software from a company or web site whose honesty or veracity you’re not sure of. If a site says you’ll need special software to use its features, don’t bite. Even if the software is well known and safe — like RealNetworks’ RealPlayer, Apple’s QuickTime or Adobe Flash — don’t get it from a link provided by a random web page. Instead, visit the Real, Apple or Adobe sites to download it manually.

6. Finally, never use security software offered to you via unsolicited email or a popup window, or that suddenly appears on your PC. Such programs are almost always scams and often install malicious spyware, adware and viruses rather than cleaning them up. In general, stick with leading security brands like Symantec, McAfee, Zone Labs and Webroot. Check the software in the reviews section of PC Magazine or the CNET web site. If it isn’t covered there, it’s probably untrustworthy.

The daunting security problems that have plagued Windows have also prompted many of its users to take a serious look at the Mac. This trend has been further reinforced by the “iPod halo effect,” in which Windows users who own and love Apple’s iPod music players are willing to consider the company’s other products. As a result, Mac sales, while still relatively small, have been growing much faster than overall personal computer sales.

Are you among the PC majority considering a switch to the Mac? Then you probably have some important questions.

How do Macs compare in quality with Windows PCs?

I believe that, at the moment, Apple makes the best computers, and the best operating system, for mainstream consumers doing typical tasks — e-mail, Web surfing, office — productivity functions such as word processing and presentations, photo organizing and editing, playing and collecting music, and editing home video.

Of all the major computer makers, Apple is the most focused on consumers and small businesses. Most make the bulk of their money, and take most of their cues, from the information-technology departments of large corporations.

Apple’s iMac G5 consumer desktop is, in my opinion, the single best home computer on the market. Its PowerBook laptops are among the top portables.

Do Macs run Windows and Windows software?

No: Out of the box, Macintosh computers run only Apple’s own operating system, called OS X, and software written by Apple and other companies that is designed to run on OS X.

You can rig a Mac to run Windows and Windows programs by installing a special, $250 Microsoft program called Virtual PC, which creates a virtual Windows computer inside the Mac. But I don’t recommend this for frequent use, because the faux Windows computer it creates is relatively slow and is susceptible to the same viruses and spyware as a real Windows machine.

How does Mac software compare with Windows?

The Mac’s OS X operating system, the latest version of which is called Tiger, is far better than Microsoft’s aging Windows XP and already boasts many of the key features Microsoft plans to include in its 2006 version of Windows, called Vista. And the Mac comes with an excellent suite of free software that’s generally superior to comparable Windows programs that cost extra.

Out of the box, the Mac has better photo, music, video and DVD — creation software than any Windows computer I’ve seen. It has a better free email program and Web browser than Windows does, a better free word processor and much better search capabilities.

About the only software a typical consumer would have to buy for a new Mac is the Mac edition of Microsoft Office. It includes versions of Word, Excel and PowerPoint that are very similar to their Windows counterparts, and a program called Entourage that is different from Microsoft Outlook but performs the same functions.

Are Macs more secure than Windows PCs?

Yes. Since the OS X operating system came out in 2001, there has never been a report of a successful virus for it — that is, a virus that has infected numerous computers, and spread from computer to computer, outside of a lab. And there is little or no known spyware for the Mac. By contrast, there are tens of thousands of viruses for Windows and untold numbers of spyware programs. Just as regular Windows programs can’t run natively on a Mac, none of these malicious Windows-specific programs can run on a Mac either.

The Mac isn’t invulnerable, but it has better built-in security than Windows, and such a small market share that virus and spyware writers haven’t targeted it yet. As a result, most Mac users have been able to dispense with running the morass of security software that Windows users must employ.

Are Mac files compatible with Windows files?

Yes. Unlike older models, the current Macs have been specifically designed for compatibility with Windows PCs. The Mac OS and software can handle, without translation or conversion, all of the common types of files you use on a Windows PC. You can copy to a Mac all your pictures, MP3 music files, text files and Adobe PDF files, and they will open right up in Mac programs. There are also free Mac versions of the Real Player and Windows Media Player, and of Adobe Reader.

Microsoft Word files also can be opened, edited and created in Apple’s free, built-in text editor. And if you buy Microsoft Office for the Mac, all Office files, including Word files, Excel files and PowerPoint files, can be opened, edited and created on the Mac. Office files created on the Mac can be opened and edited in Windows Office, and vice versa.

Some specialized files created by particular programs, like database files or financial files, won’t be usable. For instance, the Mac version of Quicken is quite different from the Windows version and uses a different file format.

For occasional use of these programs, you can install Virtual PC.

In addition, nearly all keyboards, mice, monitors and printers made for Windows computers can be used with a Mac, if they connect via the industry-standard USB or FireWire ports. Macs can also share networks with Windows PCs and even look into the hard disks of Windows computers, and vice versa.

Is there anyone who shouldn’t consider a Mac?

Yes. Serious game players should stick with Windows PCs, which are much better game platforms and can run many more game titles. People who use specialized software or custom corporate software for which there isn’t a Mac equivalent should stick with Windows. While the Mac has rich offerings in mainstream software categories, it has only a fraction of the niche software and specialized business software that Windows does.

Also, you should stick with Windows if your home computer choices are dictated by your company’s IT department and the IT department is ignorant of or hostile to the Mac, as so many are. Although modern Macs are designed to access corporate Windows networks, and many do, if your IT department won’t help you with the transition, it’s not worth the headache to switch to the Mac.

Ten years ago, when Apple was stagnant and its products troubled, I recommended that consumers shun the Mac. If Apple’s quality and innovation slip, I might revert to that position. But for now, the Mac is the best computer, with the best operating system and the fewest security problems, for average consumers.