Eternal Sunshine of the Spotless Hard Drive

There’s no other major item most of us own that is as confusing, unpredictable and unreliable as our personal computers. Everybody has questions about them, and we aim to help.

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 completely erasing a PC, installing Verizon’s Fios Internet service, and using a Firefox Web browser on an iMac.

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 am giving my PC to my sister and I would like to completely erase my files from the hard drive. How can I do this?

What you need to do is wipe out the files in a way that is more thorough than merely deleting them in the standard manner. This process is often called “wiping” files, and makes the files impossible, or at least very difficult, to recover. It works by overwriting the portion of the hard disk formerly occupied by a file’s data with nonsense characters.

You could format the disk, but that also would wipe out the operating system, which would require your sister to buy and install a new copy. So you need a program that wipes out only the folders and files you target. On an Apple Macintosh, this capability is built in. You just move the files to the trash and then select “Secure Empty Trash” instead of the usual “Empty Trash” command.

On Windows, you need add-on software. There are many programs that do this, but one that I have tested and can recommend is Window Washer, which is available at webroot.com for $30. You can find others by doing a Web search for “file wipe” or by doing a similar search at download.com.

If you install the new high-speed Verizon Fios Internet service you recently reviewed, do you have to upgrade your wireless network?

It depends. Verizon will supply you with either a wired or wireless router, the box that transmits your Internet connection. If your current Wi-Fi network is slower than the maximum speed of Fios, you should take the Verizon wireless router. For instance, if you have the 15 megabits per second version of Fios, but only have a Wi-Fi “b” type network, which works at a maximum of 11 mbps, take the Verizon wireless router and allow Verizon to install it in place of your current one. The Verizon wireless model works on the newer “g” flavor of Wi-Fi, which can handle speeds of as much as 54 mbps.

You also will need to make sure that all the PCs you are planning to connect wirelessly to Fios have “g” type Wi-Fi connections. If even one of them has “b” equipment, it will drag down the whole wireless network to the lower speed of “b.” (This doesn’t affect wired connections to computers.)

However, if your wireless router is fast enough, and you like it, you can keep it with Fios service. I did, because I am using the Belkin “Pre-N” router, which has better speed and range than any “g” router I’ve seen. I just took the plain old wired router from Verizon and plugged my Belkin wireless router into it. Others have dispensed with the Verizon gear entirely, and just plugged the Fios cable directly into their wireless routers. The main downside here is that Verizon says the routers it installs contain special software that can help diagnose Fios problems.

Can I use the Firefox browser on my iMac? I am running version 9.1 of the operating system.

Unfortunately, no. While Firefox works on the Mac, it requires the newer Apple operating system, Mac OS X, which was introduced in 2001. Firefox requires Mac OS X 10.1, at a minimum. Your computer has an entirely different, older, and much less capable operating system, which Apple has pretty much abandoned.

By the way, for Windows users, Firefox requires Windows 98 or higher. For both platforms, there also are minimum hardware requirements. Firefox also runs on the Linux operating system, and has minimum requirements on that platform as well. Requirements for all platforms are at: www.mozilla.org/products/firefox/system-requirements.

* * *

Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

Write to Walter S. Mossberg at mossberg@wsj.com