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How to erase data from an old PC or Mac

01 Feb 2011

This will be especially useful if you’re upgrading your office computers, and want to sell the old ones.
For PCs running Windows, Eraser ( is a free, open source tool which allows you to completely remove sensitive data from your hard drive by overwriting it several times with carefully selected patterns. However, some data is stored in files that are normally hidden, and you need to locate these files as well.
To do this, go to My Computer>Tools>Folder Options (in Vista, go to Organise>Folder and Search Options), then View>Show hidden files and folders. Then open the Application Data folder (‘AppData’ in Vista) and right-click to erase it. NB: the Eraser program may require you to erase files one at a time. Start with any named after heavily used programs or their developers (for instance, ‘Mozilla’ or ‘Microsoft’. If you use Outlook Express, the data is stored in a folder called ‘Identities’. Then you can wipe anything valuable in such standard, visible folders as My Documents.
Because of the volume of email stored in most computers, erasing all this can be a long, tedious task. To make it easier, create a new user account just for erasing data.
In Windows, go to Control Panel>User Accounts (in XP) or Add or Remove User Accounts (Vista).
See for advice on creating accounts in XP. Note your old account’s name, then create a new account and pick ‘administrator’ as its type. Log out of the old account and into the new one. In My Computer, go to your hard drive (C) and open Documents and Settings (XP) or Users (Vista). Right-click the folder named after your old account and select ‘Erase’. NB: this takes quite a while and is probably best left running overnight.
For Mac OS x 10.3 or later, see for advice on how to overwrite files sent to the Trash bin, to ensure they can’t be recovered, using Secure Empty Trash. For older versions of Mac OS, download Permanent Eraser from
To create a new administrator account in Mac OS X, go to System Preferences>Accounts. Again, note your old account’s name and create a new, administrator account. Log out of your old account and into the new one. In the Finder, go to your Mac’s hard drive and open its Users folder. Select your old account and use Secure Empty Trash or Permanent Eraser to wipe it.
Don’t forget to reload the original software before selling the computer.

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