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.

wipe hard drive

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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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Comments (9)
  • Daizy

    It’s true, when you delete any files, it doesn’t deleted permanently until it’s overwritten by another file. In such cases, there might be a chance of unauthorized access of your important data. You can wipe data by using Disk utility or any third party tool. Mac Disk wipe utility of Stellar Drive ToolBox helps to remove data beyond recovery from Mac hard disk and keep your data safe.

  • Darren Reynolds

    I always found a hammer was a secure way of disposing of old hard drives.. Never had one returned to me yet ;)

  • jamesbirtwistle

    I prefer the “drill through the thing” method personally.

  • themainliner

    FAIL. A secure erase multi-pass application is not necessary. One pass will destroy data enough to make data economically prohibitive to retrieve and only theoretical possible. You guys should understand this and not keep peddling these urban legends.

    • Simon Slangen

      You’re right in one way. Most simple software tools will become useless after a simple pass, but data recovery is not necessarily impossible (via hardware means) until you’ve thrown in a few additional passes for good measure.

      It’s the difference between a careful consumer (1 pass) and a prosumer/professional with sensitive data (multiple passes).

    • themainliner

      The myth that to delete data really securely from a hard disk you have to overwrite it many times, using different patterns, has persisted for decades, despite the fact that even firms specialising in data recovery, openly admit that if a hard disk is overwritten with zeros just once, all of its data is irretrievably lost.

      Craig Wright, a forensics expert, claims to have put this legend finally to rest. He and his colleagues ran a scientific study to take a close look at hard disks of various makes and different ages, overwriting their data under controlled conditions and then examining the magnetic surfaces with a magnetic-force microscope. They presented their paper at ICISS 2008 and it has been published by Springer AG in its Lecture Notes in Computer Science series (Craig Wright, Dave Kleiman, Shyaam Sundhar R. S.: Overwriting Hard Drive Data: The Great Wiping Controversy). ”

      I’m unclear as to what “via hardware means”?

      You might also want to look at – this is a myth that is thoroughly debunked and only careful consumers, still trying resolve their Windows 7 problems by ‘defraging’, are still sucked into it.

    • Simon Slangen

      I must admit, this is new material to me. Interesting, though. Thanks for posting a reference.

      Although the data isn’t “irretrievably lost”, the paper concludes that the error rate is sufficiently high so that there’s probably very little use for the retrieved data. Also, other sources note that this applies to newer (post ATA) drives with a sufficiently high data-density. This would make the multiple-pass techniques outdated, rather than “myth” or “urban legend” (which sounds unnecessarily dramatic).

      Related article.

  • Henrik Bäckman

    Just use FileVault2 from Apple on a SSD disk.
    I cannot get access to the information on my previous startdisk.
    I’ve tried at least 10 different solutions found on internet, but nothing has worked for me.

    Thank you Apple …

    • Simon Slangen

      If your private key has been deleted, there’s really nothing you can do to recover your data. In a way, that’s a good thing, because that’s what makes FileVault secure (at all).

      More on topic, the only technique I’ve encountered so far to securely erase SSD’s actually uses FileVault.

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Affiliate Disclamer

This review may contain affiliate links, which pays us a small compensation if you do decide to make a purchase based on our recommendation. Our judgement is in no way biased, and our recommendations are always based on the merits of the items.

For more details, please read our disclosure.