Completely Erase a Hard Drive

How to Erase Your Hard Drive

What's on that old hard drive? Your name, address, phone number, email, tax returns, bank account info, love letters... maybe some software or (ahem) other files you'd rather no one else knew you had. Maybe your family's info is on there, as well. How can you erase all that stuff before disposing of the drive?

You might be surprised to learn that when you delete a file, it's really not gone. All the "delete" command does is erase the record of a file's location on the hard drive, stored in the Master File Table (MFT) or File Allocation Table (FAT). That's like removing the cards from a library's card catalog but leaving the books on the shelves for anyone to inspect at random.

Okay, but formatting a hard drive erases all data on it, right? The operating system warns you about that before it executes the format command. But no, you can even recover files from a freshly formatted drive if nothing has been written over them. Data recovery software such as the Data Recovery Wizard from EASEUS.com can easily restore files on a freshly formatted drive.

To truly make your sensitive data unreadable, you have to cover it completely with new data; not just once, but several times. It's like using a pen to scratch out something you wrote earlier. A few penstrokes will obliterate old writing to the casual observer, but someone with a magnifying glass and determination can still make out the indentations of the old writing on the paper unless you scribble over it half a dozen times or more.

Tools to Securely Erase Files From a Hard Drive

Mac operating systems come with secure data erasure built in. All you need to do is move folders or files to the trash can and from the Finder menu select 'Secure Empty Trash'. Windows does not have a secure data erasure function, but several third-party utilities provide this ability.

Eraser is a free utility for securely erasing data from a Windows hard drive. It works with Windws 95/98, XP, Windows Server 2003 and 2008, Vista, and Windows 7. Eraser has a simple name but it erases files completely in several complex ways.

The default erasure method used by Eraser and many other similar programs is called the Guttmann Method after its inventor, Dan Guttmann. It overwrites data 35 times, ensuring that no one will be able to recover it. Of course, that takes a very long time. Eraser and other utilities let you schedule a secure data erasure during hours when you won't be using your computer.

A second, less thorough method is called the US DoD 5220-22.M Method. This is a standard developed by the U. S. military for securely erasing drives "good enough for government purposes." It overwrites data seven times. That will thwart all but the most determined and well-equipped data recovery experts, but it won't stop the "men in black" from the CIA, the National Security Agency, or those guys from CSI.

Years ago, I remember reading a story about one paranoid guy who lived in fear of the feds busting his door down and confiscating his computer. He had a strong electromagnet positioned near the computer, so that when the dreaded midnight raid occurred, he could flip a switch and instantly wipe the hard drives clean. I wouldn't recommend that method, because forensic tests have shown that electromagnets can leave some data intact.

I'd like to mention one final method of completely erasing your hard drive, which I have personally found to be immensely satisfying. It involves physically removing the hard drive from the system unit, and beating it senseless with a 16-lb steel sledge hammer. There's always the possibility of shrapnel, so place the drive in a brown paper grocery bag first, and wear eye protection. When you're finished, you can inspect the carnage and maybe learn a little something about how hard drives work.

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