The fact that accidentally deleted data isn’t necessarily gone forever might come as something of a relief but there are worrying consequences too. If you can’t properly delete the data on your hard disk prior to selling or disposing of your PC, or merely allowing someone else to use it, the consequences could be disastrous.

When you need to destroy data permanently, there are some rather extreme methods to render the entire disk unreadable (we'll get to these later) but these do rather depreciate the value of your PC. Here, we’ll show you how to securely delete your data while keeping your disk intact.

The method is simple enough and there are several software packages that provide secure deletion facilities. In addition to removing reference to the file in the disk’s directory, the software overwrites the areas of the disk occupied by the file with random data. See also: How to delete data using Eraser 6

The exact process differs depending on the file system and because flash drives tend to use a different file system from the hard disk, you should look for an application that supports both FAT variants and NTFS.

Delete key

Interestingly, it has been suggested that overwriting a file with random data isn’t enough. The argument is that when data is written to a disk, the resultant magnetic flux has a tiny contribution from the data previously occupying that part of the disk. It would follow, therefore, that if you extract the analog signal directly from the disk’s read/write head, and subtract the signal corresponding to the current data, you’re left with that tiny contribution from the previous data.

For this reason, some secure deletion software overwrites not just the once but many times. We discussed this with an expert in hard disk technology at Western Digital who told us that he didn’t know of anyone ever having achieved it. And while not suggesting that it was impossible, he added that it would be so expensive and time consuming that he couldn’t imagine it being attempted except by government agencies when national security was at risk.

So although there’s no reason to avoid software that claims to overwrite files 40 times, this shouldn’t be a criterion in selecting a suitable product.

Optical media

Optical discs, such as the variants of CD, DVD and Blu-ray, are quite different from magnetic or flash drives and most secure deletion products won’t touch them. For rewritable dics this really isn’t an issue since you’re not going to be disposing of them along with your PC as you would with the hard drive. If you do decide to give an optical disk to someone it’s normally specifically because you want them to have your data.

However, write-once disks such as CD-R, DVD-R and DVD+R are quite different because you’ll throw them away when you’ve finished with them. In this case, the way to prevent your data falling into the wrong hands is to physically destroy the disk. You can buy paper shredders which will also shred optical disks and if you’re paranoid you might choose that solution.

However in our experience, low-cost home shredders really aren’t tough enough for this sort of treatment and shredding CDs on a regular basis will probably contribute to premature failure.

DVD cut in half

Nobody is going to spend countless thousands on leading edge data recovery in the off-chance that a CD-R they find in your bin contains valuable data so just ensuring that it’s in two pieces will be enough. Cutting it with scissors (not your best pair, though) is one option or you could just snap it in two, having first wrapped it in a cloth to protect yourself from flying shards of plastic.

Next page: we take an angle grinder to a hard disk

Encrypt your data

None of the methods we’ve talked about so far will prevent your data from falling into the wrong hands if your PC is stolen since it’s your active data that will be at risk. If data security is a big concern it's worth encrypting sensitive files. To find out how, see our guide to Cryptainer LE.

Destroy your disks

Data can be effectively deleted from a hard disk using nothing more than a secure deletion utility. However, if you take the view that anything less than physically destroying the disk isn’t good enough, here are a few suggestions.

Bear in mind that we’re not recommending the methods here (there's really no need) and they all carry the risk of injury. Remember that some disks contain glass platters which could shatter and cut you and if your PC no longer has any value to you, it’s possible that a charity could benefit from it. With these caveats in mind, let's get on to the fun stuff.

When you remove a disk from a PC, the most easily accessible part will be the circuit board on the bottom and, as such, the easiest way to abuse the drive would be to get to work on that board with a hammer and chisel. But while that might be the simplest approach it would be futile.

This isn’t where the data is stored and if someone were to replace that board they’d be able to read your data. Instead, any attempt at destroying a disk should concentrate on the platter or platters – the silver disk(s) that you’ll see once you remove the screws (some of which may be hidden under labels, and use security heads) and take the drive apart.

Destroyed disk

Just scratching the platter(s) with a screwdriver will suffice even though it’s not a particularly satisfying experience. If you really want to release that pent-up energy, a sledge hammer would be sure to do the trick quite nicely.

If, on the other hand, you consider yourself something of a pyromaniac, a conflagration will also ensure that your data never sees the light of day again – heating up the platters to a red glow with a blow torch would be just perfect as would dropping it into the heart of a garden fire. If you have an angle grinder to hand, that will be pretty effective, too.

Hard disk cut with angle grinder

These are just a few sure-fire favourites but all that stands between you and an exciting way to wipe out your disk from the face of the earth is your imagination.