Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability. This week my mailbox contained questions about moving iTunes files to a new computer, file-compressing programs and security software.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

I recently bought an Apple iBook to replace an old Dell laptop. How do I move my iTunes music files from the Dell to the Apple?

Your iTunes music files work on both Windows and Mac machines, as does the special iTunes Library file that keeps track of play lists and the like. So, all you have to do is copy these files from the Dell to the Apple, as with any other files you want to move. In fact, even if you were moving from an old Dell to a new Dell, without changing operating systems, the process would be the same.

If you have allowed iTunes to gather all of your files into the folder called “iTunes” within “My Music,” all you have to do is copy that folder to the iBook. This can be done in a number of ways, but the best choices would be to do this via a home network or by burning the files to CDs or DVDs and then copying them from the CDs or DVDs onto the Mac. On the Mac, the iTunes folder is usually located within the Music folder.

If your music files are scattered, or are in the My Music folder, but not the iTunes folder, you’ll have to locate them before copying them. Be sure to copy the iTunes folder also, because it contains the iTunes Library file.

If you have an iPod and it contains all of your songs and play lists, you can skip these steps. Just download one of the many cheap utility programs for the Mac that will copy the contents of an iPod to a computer. Two examples are PodWorks and PodUtil, the latter of which comes in a Windows version for Windows-to-Windows transfers.

One more thing: Be sure to deauthorize the Dell from your iTunes account before authorizing the Mac, so you don’t waste one of your maximum of five slots for computers that can play any songs you purchase. To do this, fire up iTunes on the Dell, go to the Advanced menu and select “Deauthorize Computer.”

What program do you recommend the most for compression and decompression of files? Winrar, WinZip or any other program?

On Windows, I use WinZip (www.winzip.com), because of its flexibility, even though the operating system can compress and decompress files by itself. On the Mac, I use Stuffit (www.stuffit.com), for similar reasons. A decompress-only version of Stuffit came with earlier versions of Mac OS X, Apple’s operating system. The current version of OS X, Tiger, can compress and decompress files in the popular Zip compression format without Stuffit.

I run Norton Internet Security, Ad-Aware and Spybot on my computer to keep “bad stuff” from infecting my system. Yet last week a malicious program attacked my computer. It hijacked my wallpaper and put a huge warning on my desktop. My security software never knew it was there. Do I need to run additional security on my computer?

This category of spyware or adware is expanding so fast that, even with the two good anti-spyware programs you are using, attacks can happen. My only advice is to add a third, such as Webroot’s Spy Sweeper, which is my favorite. I know this is annoying, but until the spyware/adware epidemic slows down, it is often necessary for Windows users to have multiple defenses.

First, you cannot use an iPod, out of the box, to copy your music collection to multiple computers you may own. Millions of iPod owners have more than one computer, and it’s perfectly legal to copy the music you own to more than one computer. But the iPod won’t help you do this.

Second, in families with multiple iPods sharing a single computer, the iPod’s companion software, iTunes, doesn’t allow you to have multiple music libraries. With multiple libraries, each user could see only his or her own music, and could synchronize his or her iPod with that personal music library.

Apple is aware of these shortcomings, and I wouldn’t be surprised to see it solve the second one, multiple libraries, this year. But the first, the inability to use the iPod to copy music to multiple computers, is tougher. Apple was forced to cripple the iPod in this manner at the insistence of the record labels, which feared that it might be used to copy music too widely. So a fix probably requires negotiations with the labels, whose obsession with piracy has caused them to treat their own customers like criminals.

Luckily, there are solutions to both problems available today, through third-party software or workarounds. Here’s a guide to those solutions.

First, here’s how to use an iPod to copy music to multiple computers. You just have to download and install one of a number of small utility programs designed specifically to let you copy the music on the iPod to a computer. There are lots of these, for both Windows and Macintosh computers.

For Windows users, I suggest CopyPod, available for $20 with a two-week free trial, at www.copypod.net. For Mac users, I like PodWorks, available for $8 with a limited-function 30-day free trial at www.scifihifi.com/podworks. Another, similar program, which comes in versions for both Windows and Mac, is PodUtil, available for £10 ($17.66), with an unlimited free trial, at www.kennettnet.co.uk.

Once you have installed one of these utilities on your second computer, just plug in your iPod, filled with the music from the first computer. When iTunes pops up, be sure to decline when the program asks if you want to synchronize your iPod to the second computer. If you don’t decline, iTunes will wipe out your iPod’s contents and replace it with any music on the second computer.

Next, quit iTunes and launch the music-copying utility, if it didn’t launch automatically when you plugged in your iPod. It will scan your iPod, displaying all the music stored there, and allow you to copy some or all of the music onto the second computer. If you have a lot of music on the iPod, this could take awhile.

When you’re done, just quit the utility program, disconnect the iPod, and relaunch iTunes. In some cases, the utility will already have populated iTunes with the copied music. In other cases, you’ll have to use the “Add to Library” command in the iTunes File menu to bring in the music you have just copied.

How about the multiple-libraries problem? This one can be solved with some workarounds, as well as third-party software.

Suppose you want to synchronize only part of a library to a particular iPod, say mom’s iPod, in a family with several iPods. You can place the songs mom wants into a playlist called, for instance, “Mom’s iPod Songs.” Then, when mom’s iPod is connected, you can go into the Preferences settings in iTunes to designate that mom’s iPod will automatically be synchronized only with the songs in that playlist, rather than all the songs in the library.

Or, you can go into Preferences to designate that mom’s iPod won’t be automatically filled at all, but will be filled manually. Then, you could manually drag all the songs she likes onto the icon representing her iPod within iTunes.

A better approach is to download a utility program called Libra, which comes in versions for both Windows and Mac. Libra, which costs $10 with an unlimited free trial period, is available at homepage.mac.com/sroy/libra. It allows you to create multiple libraries, and to switch among them.

You just run Libra, create a library — for instance, Mom’s Library — and then select it. Next, you launch iTunes, and it comes up with only that library displayed. The first time you set up a new library, it will be empty. But you can just use the iTunes “Add to Library” command to fill it up with songs from your hard disk. You can then set up playlists that will be displayed only in that library. And you can synchronize the whole library to an iPod of your choice.

Multiple libraries can use the same songs without the need to store multiple copies of the songs.

Let’s hope Apple can build these features into the iPod and iTunes soon. Until then, the utility programs are your best bet.

• Email me at mossberg@wsj.com.