Delete hard disk data for good

Deleting data for good
A few months ago, consumer rights magazine Which? said that if you are planning to retire your computer or wish to upgrade the hard disk, the only way to be sure the data is safe from prying eyes is to smash the hard disk with a hammer.

The reason for recommending such extreme measures is that when you delete data from the PC using the tools built into Windows, it’s not actually destroyed.

Clean slate
When you select a file and press Delete, the computer tells itself to forget about that file. There’s a part of Windows called the File Allocation Table, which lists all the files on the disk and where they can be found on the physical surface of the disk.

When a file is deleted the PC removes its entry from the table, so it can no longer find it. The file, however, is still there and can be recovered using the undelete and file recovery tools available from several manufacturers.

Formatting a disk – which means wiping it completely clean so you can start afresh – is the next level up in terms of thoroughness. It physically wipes over the files on the disk to make them harder to recover.

Even then, though, there are two kinds of format: a quick format is, as the name suggests, very quick, but the downside is that it doesn’t really overwrite anything. So, again, it’s relatively easy to recover files from a quick-formatted disk. A full format is a better idea, but on a modern hard disk with hundreds of gigabytes of storage space it can take hours.

How to destroy data
So, should you really smash up your disk? Well, that’s one way to make it hard to recover the data on it, although after the story was published in Which? security experts pointed out that it’s possible to recover data from a smashed disk.

It’s also hard to smash disks as they’re surprisingly robust. It’s wasteful, too – hard disks are plentiful, but computer users in the developing world can still benefit from them. A representative of Computers4Africa, a charity that re-uses IT products, told us that the idea of smashing disks is “silly and misleading”.

A better way to erase your data properly is to use an eraser program that will physically overwrite the disk with random nonsense, or other data designed to confuse potential snoopers. Most of them even allow you to overwrite the data several times just to make sure.

One such tool is Eraser – and it’s free. Remember that with such programs you will lose everything on the disk – as you will with formatting – so back up anything you think you may need in future. Read our Workshop explaining how to use Eraser.

Why bother?
If your computer is going to be passed on to someone in the family, or if you’re giving it to someone you trust, then perhaps there’s no real need to take so many safety precautions regarding wiping the hard disk. Just delete the files, perhaps do a quick format (you’ll need to reinstall the operating system afterwards) and that should be enough.

But if you’re giving the computer to charity or selling it, then you should go a step further. Formatting the disk (a full format, not a quick one) is likely to be more than enough. Also, bear in mind that if you intend to use the same copy of the operating system on a new computer you must erase it from the old one.

Formatting is likely to stop most people from seeing your data. If what’s on the old hard disk is music and innocuous documents, it’s more than enough – after all, it doesn’t really matter if anyone else gains access to them. Most users won’t even think to try to recover data, and most of those who do will be stumped by a fully formatted disk.

But if your data is important – personal correspondence, family pictures, bank statements and so on – it’s worth blanking the disk with eraser software. This will help to ensure it is safe from almost everyone except the security services – and if they’re after your data you have bigger problems on your plate.

Our verdict
Even if you smash a hard disk to smithereens, the data may still be recoverable by someone truly determined.

In any case, smashing a hard disk is much more hassle than it’s worth. You run the risk of getting hurt, it’s wasteful and it renders the computer practically unsellable.

You can simply remove the hard disk and store it at home, then give away or sell the computer with the caveat that the new owner must supply a hard disk themselves.

Our preferred option, though, is to use eraser or shredder software to securely wipe the disk before getting rid of the computer.

It’s relatively quick (or you can leave it running overnight), easy to use and doesn’t have to cost anything.

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