Here are instructions on how to use Disk Utility to securely erase a hard drive connected internally or externally to your Mac. These instructions were written for Mac OS X 10.4 to 10.6. The process is very similar on older versions of Mac OS X but the screens will look a bit different.

Requirements – You’ll need either the Mac OS X install disk that came with your Mac or another OS X install disk that’ll boot your Mac, such as a retail copy of the Mac OS X 10.5 or 10.6 install disk.

I recommend securely erasing a hard drive before you recycle it or give it away. The instructions below include the option to re-install Mac OS X onto the hard drive at the end of the process.

If you’re securely erasing an external hard drive you do not need to use a Mac OS X install disk. Instead, you can simply open Disk Utility which you’ll find in the Utilities folder inside the Applications folder. In Disk Utility, select the external hard drive and then follow the last few steps of these instructions to erase it using one of the Security Options described below.

Background – Technically, it’s not possible to erase or remove data from hard drives. Thus “securely erasing” is a misnomer. Instead, what we’ll be doing is over-writing the data on your hard drive with gibberish, a random string of bits of data. When you securely erase your hard drive you’ll have a choice of how much over-writing you want to do. This process can take many hours if you select the 7-pass overwrite procedure. I recommend starting this process and then letting it run over-night.

• Insert the Mac OS X install disc that came with your Mac.
• Note: The disc will begin the process of installing Mac OS X on your Mac. Whether or not you actually choose to install Mac OS X is your choice, but if you do, you’ll do it AFTER you’ve securely erased your Mac’s hard drive.
• Select your preferred language from the list presented.
• When you see the welcome screen for the Mac OS X Installer, go to the menu named Utilities and select Disk Utility.
• In the left pane of the Disk Utility window, click on the hard drive you want to erase.
• In the right pane of the Disk Utility window, click the Erase tab.
• Click the Security Options button.
• I recommend that you select the 7-Pass Erase options, but you could choose the 35-Pass Erase option. Here’s my description of these options.

Don’t Erase Data— This option does not provide any security. This option only over-writes the directories on the hard drive. Your files could still be recovered.
Zero Out Data— Provides a pretty good level of security. All of your files are over-written with a string of zeroes. There are forensics utilities that in theory could retrieve some data.
7-Pass Erase— Provides a lot of security. This is considered sufficient by government standards to erase data from a disk. It writes a random string of ones and zeroes over your data files seven times. It may take several hours or more to complete this process.
35-Pass Erase— Provides the maximum amount of security offered. This option takes an extremely long time, possibly more than one day.

• Click the radio button in front of 7-Pass Erase.
• Click OK.
• Click the Erase button next to the Security Options button.
• Confirm you want to erase and the process will be begin.
• If you want to install Mac OS X then go to the Disk Utility menu and select Quit after the erase is complete.
• You’ll be taken back to the Mac OS X Installer welcome window. Click Continue.
• Agree to the software license.
• In the “Select a Destination” window click on the icon for the hard drive which you just erased and then click Continue.
• Click the Install button to start the installation process. Depending upon the speed of your Mac and the version of Mac OS X which you are installing this process could commonly take anywhere from 20-60 minutes.

I recommend that every iPhone owner enable the password protection feature built into the iPhone. Then, if you ever lose your iPhone others won’t be able to view your iPhone’s contents or run up your bill by placing lots of calls.

Here’s how you can enable this feature:

• Turn on or wake up your iPhone.
• Tap on the Settings icon.
• Select the General category.
• Tap on Passcode Lock.
• You’ll be prompted to enter a 4 digit passcode (aka password). Then you’ll be asked to enter it again to make sure you didn’t make any typos.
• Finally, tap on Require Password and select how quickly your iPhone will require you to enter your passcode after being idle. I recommend “After 5 minutes.”

This should give you peace of mind in case you lose your iPhone around the house, around town or while traveling.

If you have a MobileMe subscription then you should also make sure that you have turned on your iPhone’s “Find My iPhone” feature. More on this in my next blog article.

Do you have personal or sensitive information about yourself or your clients on your Mac? Things such as credit card numbers or passwords? If so, I recommend storing this information in a special kind of file known as an encrypted disk image. I store a list of my own passwords and other sensitive information in such a file on my Mac laptop. This file is always readily available while still being inaccessible by others, even if my laptop were stolen.

Without getting very technical, disk images were invented as a way to make a backup copy of a disk such as a floppy or CD, but other uses have emerged over time. Mac OS X lets you create a blank disk image that can be thought of as an empty folder. Additionally, this file can be encrypted which requires a password when you open it. Thus, in an over-simplified way, you can think of an encrypted disk image as a password-protected folder.

Read my next blog post for step-by-step instructions on how to create and use an encrypted disk image on your Mac. After creating your own secure disk image, copy the files that you want to protect into this disk image. For example, if you keep a list of passwords or other sensitive information in a Word or Excel file, copy this file into the secure disk image. Once you’ve confirmed that this file is inside your disk image, then throw away the original file so it’s no longer sitting unprotected on your Mac’s hard drive.