Erasing Macintosh Hard Drives

Warning: Please ensure all of the data from the computer is backed up since there will be no way to recover your data after you have finished this procedure. You can write the data to a CD, USB stick or other storage device. After backing up please ensure that all removable storage media (floppy disks, CD, DVD, Jazz, Zip) have been removed.


For Mac OS 10.3 and above (earlier versions, see below), secure data removal can be done natively with the operating system using the Disk Utility. You will need to boot from an OS installation disk and then launch Disk Utility from the Utilities menu.

  1. In Disk Utility select the Erase tab.
  2. Select the drive you need to format under the left hand menu; you need to select the actual drive rather than the partition. 
  3. Click the Options button. The following are the available security options:
    • Don't Erase Data: This option only rewrites the headers on the disk. Files can be recovered by disk utilities, and other advanced recovery software.
    • Zero Out Data: There are utilities that, albeit expensive and time consuming, can retrieve zeroed-out data.
    • 7-Pass Erase: This is considered sufficient to erase data from a disk. It writes random data over the disk seven times. It may take several hours or more to complete this process.
    • 35-Pass Erase: This makes it absolutely impossible to regain any data off the drive. This option takes an extremely long time, possibly more than one day.
  4. Click the radio button in front of 7-Pass Erase.
  5. Click OK.
  6. Click Erase.

The procedure will take quite a long time; typically for a 40GB Hard Drive it may take up to 36 hours to complete. The individual who cleared the hard drive should fill out the certification form for asset disposal.

To enhance day-to-day security, there is also the option with OS X 10.4 or later to Secure Empty Trash. That is to say to overwrite a file in a secure way rather than just remove it from the contents table. This is a considerably more secure way to remove data on a day-to-day basis but is not a substitute for securely formatting a hard drive. Secure Empty Trash is located in the Finder menu (and it is only selectable when there are items in the Trash).

This item can take a number of minutes to complete depending upon the number and size of files being trashed.


Earlier versions of OS X
The Secure Empty Trash function does not exist in OS 10.0/10.1/10.2. However, there are some third party utilities which carry out the same function. These include:

Permanet Eraser
This carries out the same function as Secure Empty Trash and likewise the data is not recoverable once it has been erased.

Darik's Boot and Nuke (DBAN)
A popular open-source utility available for the PowerPC platform in general that will erase hard drives.

OS 7, 8, 9
Within Mac OS 7/8/9 there is no in-built function for data removal, furthermore the most comprehensive disk format is to zero all data which is still not overwriting the disk sectors. There are a number of third party utilities which can perform this function. Some are listed here. IST does not offer support for these products, information is given on an advisory basis only.

The Eraser Pro 2.7.0 (Shareware)
A utility which can seecurely erase and securely format disks. Works with OS 7 +

ShredIt (Shareware)
ShredIt shreds files, folders, free disk space, deleted files, hard drives, and external hard drives. Works with OS 7, 8, 9, and 10.  

Disclaimer: This information is provided as an information service only; it is neither an endorsement nor a recommendation of products.