Hard Drive Erasure

Are you thinking of donating or recycling an old computer? Better make sure you first erase (or "wipe" or "format") your data. While simply deleting all of your files is one approach, it is not very secure. Did you know that when you delete a file, the contents of the file remain on your hard drive? In fact, deleting a file simply modifies the directory that references the location of the file contents and tells the directory that the space is available to be re-used. That's why if you accidentally delete a file, it is often possible to un-delete the file. But if you delete a file and then save a lot of other information to the hard drive, then chances are that new information may have over-written the same physical location where your deleted file had previously resided, thereby making it far more difficult (but not necessarily impossible) to recover. That is the basis for a variety of hard drive wiping algorithms. In fact, the more times you over-write previous data, the more difficult it is to recover that data in a meaningful way.

In this post, I will address some simple ways to erase hard drives on Windows and Macintosh systems. Needless to say (but I'll say it anyway), make sure you have backed up any information that you intend to keep before wiping your hard drive. Then after you've verified that you've backed up the desired data, check again. Are you sure now? OK, then consider making 2 or more backup copies because when it comes to preserving data, redundancy is a good thing. Are you totally sure now? Just checking. Once you apply one of these techniques, your data will be gone forever. Alright, on with the discussion.

First, a discussion about wiping methods. The quickest method is a 1-pass erase where you simply write zeros over the entire hard drive. While this is far better than simply deleting your files, it is theoretically possible to apply forensic technology to examine the residual magnetic properties of your hard drive and recover the overwritten data. So as long as you're going down this route, you might as well go for at least a 3-pass erase, where most algorithms write a 10101010 pattern on the first pass, followed by a 01010101 pattern on the second pass, and then a random pattern on the third pass.  For the paranoid, there is also a 7-pass option. For the extreme paranoid, there is a 35-pass (Gutmann method) option--geez, what kind of data do you have on your hard drive to need this? Nevermind, I don't want to know. The 3-pass option takes (you guessed it) 3 times as long as the 1-pass option, and the 7-pass option takes... ahem, you get the point. So depending on how large your hard drive is, be prepared to leave it running for a long time (eg, hours or even days depending on how hard drive size and number of passes).

On Windows operating systems, I recommend using an application called Darik's Boot and Nuke (DBAN). A free download is available at www.dban.org. Simply retrieve the latest version and burn it to a CD or DVD. Then boot your machine to the DBAN CD or DVD. Depending on what machine and operating system you have, you might be able to set a target boot destination or get into the machine BIOS by pressing a certain key or key combination upon startup. From there, you can select the wiping method. There are 1-pass, 3-pass, 7-pass, 35-pass, and other options. When finished, you can install an operating system on your hard drive if desired.

On Macintosh operating systems, if you have a recent operating system (e.g., OS X 10.10 Yosemite and OS X 10.9 Mavericks) simply restart your Mac and hold down the Command and R keys. At the menu, select Disk Utility, select the hard drive, and click the Erase tab. You'll have options for 1-pass (Zero Out Data), 7-pass, and 35-pass wipes. After the drive is erased, you'll have the option to re-install the operating system. For older Mac operating systems, you should have an installation DVD or CD that came with your computer. Boot into the DVD or CD (depending on your machine, you may have to hold down a different key or key combination to boot into the CD/DVD drive) to access Disk Utility and erase away.

Well, there you have it. Hopefully these approaches will keep your personal information secure. By the way, if the above methods are too complex or time-consuming for your taste, the alternative is to just smash your hard drive with a hammer--it is probably a faster method and definitely way more fun, but the recipient of your old computer will not have a functioning machine. :-) If you have other recommendations for wiping Windows and Macintosh computers, leave a comment below!