How To Securely Wipe A Hard Drive [Mac OS X]

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wipe hard driveThe new MacBook lineup is upon us, and the hardware is delicious, albeit with a hefty price tag. Perhaps you’ll use this chance to get a new computer. Since Mac computers have great resell value, you’ll want to put your current computer back on the market.

However, before you hand over your laptop to a complete stranger, you’ll want to make sure it’s been scrubbed clean of all personal and confidential files. If you’re big on privacy, simply formatting the disk won’t do. Instead, you’ll want to securely erase it, rendering all future attempts at data recovery futile.

There’s a large arsenal of tools that focus primarily on hard drive security, but everything we really need to securely wipe a hard drive is already present on Mac OS X.

How to Securely Wiping a Hard Drive

When you ‘delete’ a file, the space it occupied on your hard drive is marked as ‘available’, but the actual data remains accessible until it’s overwritten by another file. The same thing happens when you format a disk; some markers are deleted, but most of the data is still there, if you know where to look.

Secure erase works by repeatedly overwriting every memory position on your hard drive with zeroes, or random numbers, until even the biggest tech whiz can’t recover the original data.

Important: This information applies to regular hard drives, not to SSD‘s. In fact, Mac OS X has disabled secure erase functionality for solid state disks.

Secure Erase Using Disk Utility

The functionality we’re looking for is embedded in Disk Utility, which is located at Applications -> Utilities -> Disk Utility. With the application fired up, select the disk or partition you’d like to erase, and open the Erase tab. At the bottom of the window, you should see a button with Security Options. If the button is blanked out, you’re probably viewing your main partition, and should read the item below.

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wipe hard drive

The security options offers you a tradeoff between speed and security. By default, erasing a disk is faster than you can say “insecure”, but the more security you crave, the longer it’s going to take. In older versions of Mac OS X, you could write over the data 35 times, which is pretty ridiculous. In Lion, the maximum is 7 times, which still meets the US Department of Defense’s security standards.

how to wipe hard drive clean

Once you’ve selected your flavor of security, just hit the Erase… button, and off you go. If you have a large hard drive, my advice would be to use the seven pass option overnight, so you can wake up to a squeaky clean hard drive in the morning.

Securely Erase Your Primary Disk

You can’t wipe the hard drive or partition you’re currently using, which is hardly surprising. Luckily, if you’re looking to erase your primary disk, we can open Disk Utility without starting Mac OS X. Once you’ve completed the steps below, go back to the previous item about using Disk Utility to securely erase your hard drive.

If you’re using Mac OS X Lion (10.7) or later, praise your luck, because it installs a recovery partition on your hard drive. Restart your computer, and hold down option (alt). This brings you to the boot menu shown below. Choose Recovery HD and press enter. You can also hold option + R during startup to directly boot the Recovery HD. When it’s finished loading, you can select Disk Utility from the Mac OS X Utilities window.

wipe hard drive

The other option, which works on all versions of Mac OS X, is to use your Mac OS X installation DVD. If your computer doesn’t automatically boot from the disk after restarting, you can hold down the option (alt) key, and select the installation disk in the boot menu. When the installer appears, first select your language, and choose Disk Utility from the Installation menu.

Do you take any additional data security measures on your Mac?

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