Estimated time to complete: 5 mins

Deleting a file from your computer is like opening a book and scratching out the name of a chapter in the table of contents. The chapter isn’t really gone, just the information about how to find it is. To really wipe out the information in a book, you would turn to the chapter itself and scribble over the words until they were illegible.

When you delete a file by emptying the Trash folder, the only data erased from the hard drive is a small bit of information that points to the location of the file. The actual file remains on the hard drive where it can be retrieved with common software tools.

Using Secure Empty Trash or the Disk Utility will prevent the recovery of deleted files by overwriting the file data with meaningless data. Securely erasing data with these procedures is considered a best practice for eliminating sensitive data, and is a critical task to perform if you donate or sell your computer.

Before You Proceed:

These Security Shorts are intended for non-technical users who manage their own computers. If your computer is managed by an IT department, do not proceed. Contact your IT administrator for further assistance.

These examples require a Mac running OS X 10.3 or later. The screen shots will vary depending on what operating system you are using. The screenshots shown are of a Mac running OS X 10.4.

Step 1: Delete Using Secure Empty Trash

Using the Disk Utility to Prevent Recovery of Deleted Files

Troubleshooting

Step 1: Delete Using Secure Empty Trash

1. Drag the items you wish to delete into the Trash at the end of the Dock.



Note:

At this point, any files or folders you drag to the Trash will remain there until you empty the trash. If you change your mind, you can still retrieve items by clicking the Trash icon to open the window, and then dragging items you want back to your home folder. Even after you empty the Trash, deleted files may still be recovered by using special data-recovery software.

2. To delete files so that they cannot be recovered, click the Trash icon. You will see that your file is now in the Trash folder. Make sure that there is nothing else in the Trash folder that you don’t want to permanently delete.



3. Choose Finder > Secure Empty Trash.



A dialog box appears with the question "Are you are sure you want to erase the items in the Trash permanently using Secure Empty Trash?" Choose OK.



Note:

The Secure Empty Trash option performs a 7-Pass Erase, which meets current U.S. Department of Defense security requirements for general files. Depending on the size of the file, this process may take some time.

Using the Disk Utility to Prevent Recovery of Deleted Files

Securely erasing data with the Disk Utility is considered a best practice for eliminating sensitive data, and is a critical task to perform if you donate or sell your computer.

Note:

Erasing free disk space does not erase the other files on your disk. Also, depending on the amount of free space on your disk, this process may take some time.

1. Click on the Finder icon on your dock, then Applications > Utilities > Disk Utility.



2. In Disk Utility, select the disk or volume in the list which contains the free space you want to erase. In this example, the Macintosh hard drive is selected.
3. Click the Erase tab.
4. Click the Erase Free Space button.



A dialog box opens with Erase Free Space Options: Zero Out, 7-Pass, and 35-Pass. Zero Out writes a single pass of 0’s over the portions of the disk being erased, while 7- or 35-Pass will write and delete random 0’s and 1’s for the specified number of passes. While the multi-pass erase options take time to run, they are highly secure methods for ensuring that your data cannot be restored.

Note:

35-Pass is recommended for very sensitive data. The Secure Empty Trash option performs a 7-Pass Erase



 

5. Select an option that works best for you, then click Erase. Make sure to give yourself plenty of time for the mechanism to run, especially the multi-pass methods.

Troubleshooting

1. Select the item and choose File > Get Info.
2. Deselect the Locked checkbox in the General pane.

If you do not own the item, you may need to provide an administrator's name and password to put the item in the Trash.