Prevent Identity Theft and Snooping by Securely Erasing Your Old Hard Drive

Data lives on long after you empty your trash can. With simple recovery applications, newly deleted files may be recovered and opened. With more sophisticated programs, files you deleted years ago may be recovered and read. With all that we do on our computers now, our hard drives are full of personal and confidential details. When you sell, donate, or otherwise get rid of an old computer, you are going to want to securely erase all data from the drive before getting rid of it.

Fortunately, with newer versions of OS X this is easy to do. With older versions of OS X as well as OS 9 and below, it can get tricky but still possible. I’ll also go over some methods for non-working drives and what can be done with them.

What is Secure Erasing?
Secure Erasing is writing either zeroes, ones or a random pattern to every data holding piece of the hard drive. This necessary because when you delete a file, it really isn’t deleted. What happens is the OS deletes the marker for the file within its directory. Over time, the OS will overwrite the data but it may never fully overwrite the entire file. With file fragmentation, it is possible the file will be in many different places on the drive.

Recovery programs will ignore the directory, read the disk and attempt to recover any files that it can completely recover. More sophisticated recovery programs and sector editors can still get to the data and the read parts of overwritten files that are still intact. Forensics labs can even recover files that have been overwritten. This is why the recommended way to Secure Erase a drive is either the 7 Pass method or the 35 Pass method.

Note: The more passes you add to the secure erase cycle, the longer it will take. Also the larger the drive, the more time it will take. Plan on a 7 Pass erase of a 60GB drive taking a few hours.

OS X Tiger and Leopard (10.4-10.5)
1. Start up your computer you would like to erase either from the CD/DVD that came with it (Hold down ‘C’) or in Target Mode (Hold down ‘T’).
– If you started in Target Mode, connect the computer to another computer running 10.4 or higher via firewire.

2. Run Disk Utility. On the CD/DVD it is on the Menu Bar under the Tools option.

3. In Disk Utility, choose the drive you would like to securely erase.

4. Click on Options.

5. Choose your erase method – 7 Pass (Recommended) or 35 Pass (Paranoid).

Disk Utility - Secure Erase Options

Click here for technical data on each method.

6. Wait a few hours or more depending on drive size and method chosen.

OS X Jaguar and Panther (10.2.3-10.3)
In OS X version 10.2.3 (Jaguar) to version 10.3 (Panther), the only secure erase option is a one pass of zeroing out the data. For more security it is recommended that you zero out the data at least 3 times.

1. Start up your computer you would like to erase either from the CD/DVD that came with it (Hold down ‘C’) or in Target Mode (Hold down ‘T’).
– If you started in Target Mode, and are connecting the computer to another computer running 10.4 or higher, follow the previous instructions.

2. Run Disk Utility from the CD. It will be on the Menu Bar under the Installer option.

3. Choose the Drive you would like to erase and click on the Erase tab.

4. Select Options and check the checkbox for “Zero all data”.

5. Click OK and Click Erase

6. When finished, repeat this process at least three times.

OS X 10.1 and System 7.5 – OS 9
Since OS X 10.1 wasn’t really as complete as 10.2 (Jaguar), the Zero all data function isn’t present. Fortunately, we have the option of booting into OS 9 which does support this. If you have a system thats at least System 7.5 up to OS 9, follow these instructions.

1. Boot from the System 7.5 up to OS 9 CD that came with the computer.

2. Choose Drive Setup from the Utilities folder

3. Choose the Functions option and then Initialization Options.

4. Choose the Zero all data option.

5. When finished, for a more secure erase, repeat this process at least three times.

Non-Working Drives
Its nice to have the built in secure erase options with the Mac OS. Unfortunately, they only work if the drive itself works. What happens when there has been damage to the drive and its unusable? All your data is still on the drive, even if it is broken. Most people think that smashing it with a hammer is the proper solution. Its not.

Although juvenilely fun, not only is the hammer smashing grossly unfriendly to the environment, it is also dangerous. You want to recycle this drive properly rather than have it rot in tiny bits in a landfill, leaching metals into ground water. There is a better way, but it involves a Torx screwdriver set, a strong magnet, some fine/superfine sandpaper and removal of the drive from the computer. Easy for a desktop and the MacBook line. Difficult for the iBook, Powerbook, MacBook Pro and Mac Mini lines. For detailed instructions on removing the drive, visit

Once you remove the drive, use your Torx screwdriver set to open up the drive itself and remove the platters. Since the drive is broken and you don’t care for what is on it, you don’t have to be super careful. For a good drive that you would like to use again or recover something from, do not do this.

Take the platters and pass the magnet over them. Have the magnet touch the surface. If you are super paranoid, or the magnet is weak, lightly sand in a circular motion, both sides of the platters. You don’t even have to sand much, just one or two passes over the platter and it will be damaged enough to render it unreadable.

Put the drive back together and back into the old computer and recycle it properly.

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One thought on “Prevent Identity Theft and Snooping by Securely Erasing Your Old Hard Drive

  1. Very nice posting. Formatting or deletion doesn’t remove data permanently. With the help of data recovery software anyone can recover your precious data. To avoid this situation you can use stellar drive utility which wipe data beyond recovery with the help of advance algorithm.
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