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.

[UpdateNov2014: If your Mac has OS X 10.7 or newer installed then Apple didn’t give you an OS X install disc with your Mac. Instead, you can startup your Mac from its Recovery Partition and then use its copy of Disk Utility to securely erase your hard. Click one of the links below to follow the appropriate instructions for the type of hard drive that you have. If you’re not sure which type of hard drive you have, then you most likely have a mechanical, spinning, hard drive.

If your Mac has a mechanical, spinning hard drive and OS X 10.7 or newer then use these instructions.

What the “Erase Free Space” feature did (and still does in prior versions of Mac OS X) was overwrite the free space on a drive to prevent file recovery, adding a layer of security and privacy to file removal, much in the way that Secure Empty Trash performed a similar function of overwriting data after removal. 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.

If your Mac has a solid state drive (SSD), aka Flash Storage, and OS X 10.7 or newer then use these instructions.]

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 overnight.

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.

File Eraser For Mac

Update Oct 2014: In OS X 10.9, Mavericks, the 35-pass erase is no longer an option. Also, there are no longer radio buttons to select how many passes to erase. There is a slider that goes from Fastest to Most Secure.

Why Paragon Disk Wiper for Mac?

Eraser For Mac Free

Paragon Disk Wiper for Mac allows to create a bootable USB-flash drive or external hard drive that will help you to completely erase a whole hard disk, a separate partition or just clean free space. After booting your Mac with the bootable media you will be able to use Wipe Wizard to irreversibly remove your confidential data.
Paragon Disk Wiper for Mac supports all Intel-based Macs, providing the possibility to quickly and efficiently sanitize the hard disks in order to protect valuable business information and also because there is, in the most countries, a legal obligation to do so.

Key Features and Benefits

Flash Drive Eraser For Mac

Features	Benefits
Support for Mac OS X	Works with OS X 10.7 and later.
Comprehensive wiping	Wipe exactly what you need – hard disks/separate partitions (primary, extended, logical).
Ten different disk sanitization algorithms support	Irreversibly destroy all on-disk data in compliance with major national government and military data erasure standards, as well as the most comprehensive academic wipe algorithms, thus providing maximum level of security (US DoD 5220.22-M, US Navy standards NAVSO P-5239-26, British HMG Infosec Standard No.5, German VSItR Standard, Peter Gutmann’s algorithm, Bruce Schneier’s algorithm, etc.)
Wiping SSD	Wipe SSDs of most manufacturers.
Powerful Paragon`s algorithm	Improved disk wiping technology (SSD Trim) guarantees irreversible secure data destruction on SSD storage devices.
Flexible customization option	Create your own wipe algorithm with minimal effort – define up to 4 wiping patterns, number of passes for each wiping pattern and for the group of patterns, thus resulting in over 40000 possible number of passes.
Efficient operation	Minimal effect on the system performance.
Easy to use	Simple wizard driven engine.
Basic partitioning operations (create, delete, format)	Optimize the management of your hard disks.
Wipe report with extended hardware and system information	Be well-informed about the results of the wipe operation to verify when wipe operations have been successfully accomplished.
Logging of bad blocks (corrupted sectors)	Be informed that these sectors may still contain classified information.
Support of latest HDD standards Deluge also feat