Your hard drive is out to get you.

Recently a news story surfaced about a married couple who had their hard drive replaced at a Best Buy. The employees promised to destroy the old hard drive. Evidently, one of the employees had a different idea, because some months later the couple got a call from a man at a flea market. He’d bought the couple’s old hard drive at the market, found their personal data, and wished to return it. The story had a reasonably happy ending; the couple got their hard drive back, but there’s no telling who had the drive (and their personal information) before the drive wound up at the flea market.

Then there’s the sordid tale about the man who sold a defective laptop on eBay, yet neglected to wipe the hard drive. This turned out to be a remarkably bad idea. The disgruntled buyer dug through the hard drive, discovered that the seller had a penchant for both pornography and secretly photographing the legs of miniskirt-wearing women on the train, and posted these hideously embarrassing pictures, along with the seller’s name. Needless to say, this has become something of an epic Internet meme, the eBay Negative Feedback From Hell.

There are all sorts of conclusions we can draw from these stories. The world needs better methods of encrypting data, and our current e-commerce system, reliant upon Social Security and credit card numbers, is dangerously insecure. However, these are all long-term changes. There’s one immediate and practical application:

Unless you want your identity stolen or your personal failings displayed on the Web for all to see, it is vitally important to destroy the data on your old hard drives!

Fortunately, there are several ways to do this.

Formatting a hard drive as a method of data disposal is not recommended. It’s a popular misconception that formatting a drive wipes the data. This is untrue; formatting merely destroys the drive’s index. Until the drive is actually overwritten, the data is still there. Anyone with Norton Utilities, or a variety of other programs, can retrieve the files. To destroy the data on the drive, it’s necessary to overwrite the drive with gibberish, several times, until the original data is irretrievable. There are several utilities designed to do just that.

One of the most popular hard-drive wiping programs right now is Darik’s Boot and Nuke, created by Darik Horn. Available for free, DBAN runs off a Linux kernel, and totally wipes any hard drive through a combination of the Gutmann Method and the Mersenne Twister. The Gutmann Method employs multiple overwrites of a hard drive with random data, while the Mersenne Twister provides pseudorandom numbers for that purpose. On a large hard disk, DBAN can take most of a day, sometimes longer, to run, but when it’s done, the data is almost totally destroyed. (Data destroyed by a Gutmann wipe can theoretically be recovered, though it took the FBI and the NSA working in concert using extremely advanced data-recovery tools. A hard drive wiped by DBAN is almost certainly out of the average identity thief’s reach.)

For the truly paranoid, the only certain, irrevocable way to destroy data is to physically smash the hard disk itself.

Speaking from experience, I can say this is harder than it looks.

Your average desktop hard drive is a metal shell about the size of a paperback book, while a laptop drive has about the same dimensions as a deck of cards. The metal shell protects the drive from dust, and houses the logic boards, the motors, and the drive heads. The disk itself will consist of a series of thick metal platters. Those are the important parts; the platters house the data itself.

Therefore, it’s necessary to open the drive case before pounding on it with a hammer. Whacking away at the case might be cathartic, but it does little actual damage to the platters. You’ll need to take the hammer to the platters themselves.

The type of hammer is also important. A rubber mallet is totally useless for data-destruction. A claw hammer is good, but it can take five to ten minutes of vigorous pounding to satisfactorily smash the platters. A sledgehammer is the best of all. Ideally, you’ll want a twenty to thirty pound sledge, something you need to lift over your shoulder to swing properly. The cumulative force of several sharp blows will quickly render any hard drive platter unreadable.

For those preferring more finesse, drilling holes through the platters is a favored method. Keep in mind that a power drill is a dangerous tool; it can drill through skin and flesh with minimal fuss, and you’ll want safety goggles to guard against flying metal shavings. If you have access to a blowtorch (and the training to use it safely), consider using it to destroy old hard drives. A half-melted drive platter is useless for data storage (though it does make a spiffy paperweight).

In the modern age of phishing, spam, eBay fraud, and identity theft, paranoia must be your watchword online. Extend this paranoia to your old hard drives. Safe online practices will do you little good if someone pulls all your information from the old computer you left at the recycling center.

After all, which is cheaper? Years spent restoring your credit score, or a twenty pound sledgehammer?