An article on about cell phones not keeping your secrets, and my own recent purchase of an Intel iMac got me thinking about what I needed to do if I ever decided to sell my PowerBook. Well in all honestly it was my sister who asked the question. I think it’s because once she saw my new iMac and she has a Bondi blue model, she started thinking about upgrading her own computer!

What do you do when you’ve decided it’s time to buy a new computer and you don’t want to keep your existing one? A couple answers come to mind—recycle, donate, sell—but there’s one important step you need to take regardless of which avenue you choose. You need to erase all your personal data.

Don’t think that simply by putting all your sensitive files in the Trash that emptying it is enough. Destroying data is difficult and even damaged disks can yield secrets when inspected by forensics experts. Okay, so maybe that’s a bit extreme but if your computer will have new owners consider it a courtesy to the them because it will improve the computer’s performance. Or you could keep in mind the “6 degrees of Kevin Bacon” game in that someone you know will eventually find your personal data. Okay, that last one is WAY out there and I’m skewing how the game supposedly works, but I couldn’t resist! 😉 What’s really important to delete? Internet files and saved data.

Web browsers store a sundry of information about your internet use, most of it kept to save time and bandwidth when accessing favorite websites. The code and graphics that make up all the sites recently visited are stored, and many sites store small text files (cookies) on your computer when you view them, and these can be very useful, for storing login information to sites that require registration. Deleting all the cookies is an option, but you will have to re-enter usernames and passwords on sites that require them.

The web page history is another file you might want to remove. When a web address is typed into the browser, it’s saved and will appear when you begin to type it into the address window again. The pages that have been visited are stored in folders filed by date – clicking the links within the folders will take you straight to the page. History can be very convenient for reaching websites that are often visited, but it also provides a list of your web habits to anyone else using the computer. When deleting any web information, the first thing to check is that you’re not online; there’s no point clearing the files if a web page is adding new ones at the same time. Shut down all other programs as well.

Files saved and stored on a hard-disk are more difficult to remove permanently but thankfully Mac’s have a great utility called Disk Utility (located in Applications/Utilities/). There are 2 methods to use in Disk Utility for erasing everything on your hard drive. The first is to choose the Erase tab and click on the Erase button. The chosen disk will appear empty but in actuality what’s gone is only the catalogue directory, or the “pointers”, to the files. To make sure your data is truly gone, click on the Security Options. You’ll see a number of erasure options, including Zero Out Data, 7-Pass Erase, and 35-Pass Erase. When you select multiple passes, the drive is erased multiple times to remove all data traces; naturally the more passes the more time it takes.

Here are a couple documents from Apple on using Disk Utility:

Disk Utility 10.5 Help

Mac OS X 10.4: About Disk Utility’s secure erase options

While thieves may be targeting big companies to steal information, there’s not AS much to worry about for a home user. However, given the rise in Identity Theft, it’s in your best interest to securely erase your personal information. Plus it is a nice courtesy to take your data off an old computer. The new user wants to create their own collection of personal data, and if the browser constantly tries to put your personal details into web pages, it will make annoying surfing for the new user; not to mention a security risk for you. Deleting data helps make the computer run better, saves storage space and, most importantly, makes sure you are in control of what’s seen and what’s not.


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