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Securely erase the disk contents

Computers are are very reliable machines and they often work for many years. Although we often complain about them, they lose files, they won't start up, or exhibit some other problem, these are more often than not software issues and the hardware is fine. Disk drives, motherboards, CPUs, power supplies and all the other components inside the computer are actually quite reliable.

We often outgrow our computer before it completely fails and this is usually the main reason why they are replaced. The operating system we want to upgrade to or the software we want to run requires more powerful hardware, so we replace our aging computers with brand new ones fitted out with the latest technology.

What do you do with the old computer though? You could dump it, take it to a recycling point, give it to a friend or relative that is running less demanding software, or even sell it. Hang on a minute though, doesn't the disk drive have lots of personal information on? It may have your contacts, emails, documents, music, videos, and more. The web browser may have remembered the passwords to all your online sites and services and might even automatically log you in when you visit Facebook, Twitter, and other websites. You don't want whoever gets your old PC to be able to access all this do you? Of course not. You must clear all your personal information off the computer before getting rid of it, selling it or giving it away. But how do you do this? Here are some suggestions.

Erase the disk
The first thought that comes to mind is to somehow erase the whole disk drive. This sounds easy, but it isn't as straightforward as you might think. You cannot delete files that are being used and when the computer is up and running, lots of files are in use.

The only way to delete the whole disk drive is to start the computer from either a second disk drive, which could be a USB drive, or a CD/DVD. There are several CD/DVD boot discs you could use and one is Darik's Boot and Nuke. This must be written to a CD-R using CD burning software that can write .iso files (most can). You then start the computer with the disc in the drive. Most computers are set to boot from a CD if there's a suitable one in the drive, but you may need to go into the BIOS setup and enable it if it isn't (press Del, F1 or some other key just after switching on).

Darik's Boot and Nuke

There's no mouse control or pretty graphics, you use the keyboard to select menu options and it's visually dull, but it gets the job done. Hit Return at the first screen, then space at the second to select the wipe function. Press M to change the method, but the default is fine. F10 starts.

Install Linux
If you are dumping the PC then erasing the hard disk drive is fine, but it's not a good idea if you intend to pass it on to someone else. The person you sell or give the computer to will expect it to be working. They will want to switch it on and use it. You don't want to leave all your files on it though, so one possible solution is to install Linux.

Go to DistroWatch.com and you'll find links to hundreds of versions of Linux. There's a chart showing the most popular ones and it includes Mint, Ubuntu, Fedora and so on. Pick one, download the .iso file and burn it to a CD or DVD. Boot up the computer with it in the drive. You'll probably get the option to install it or boot to the desktop from the CD/DVD. After booting up there are more options to install it. Make sure you choose to use the whole hard disk and overwrite Windows, don't install Linux alongside it in a new partition.

The idea is that Linux will overwrite your old files so no-one can access them and the person you sell or give the computer to will get a fully working computer. Technically, an expert could recover some files even after installing Linux, but it's beyond most people. You can always install Linux after using Darik's Boot and Nuke if you're worried.

Erase your files
Suppose you want to sell or give your computer to someone with Windows fully working. In this case you would need to erase your files and data, but without erasing any essential Windows files. This is the least secure way of handing over your PC to someone because it's hard to find all the places Windows might hide information.

Click Start, right click Computer and select Properties in Windows Vista and 7. Click System Protection and turn off System Restore for the hard disk drive. (In XP, click the System Restore tab in the dialog.) This stops it making backups. Then go to the Control Panel and into User Accounts. Create a new administrator account (no password needed), then restart Windows and log on with the new account. You can then go back into User Accounts and delete your old account. You'll see an option to delete all your files too.

Windows and most programs store personal data in your home folder, so deleting your account deletes your files. You should check that other software you have installed does not still have personal information in though. For example, start your web browser and make sure it doesn't auto-login to Facebook, Twitter, your online bank and so on. It shouldn't because you're in the new account you just created, but it's best to check.

Now you need a utility that will erase files and free disk space. A useful free utility is Eraser, but there are others. Use it to erase any remaining files, such as in the Shared/Public folder. You may have photos, videos and other files in there. Then use it to erase the free disk space so that deleted files in your old account cannot be recovered.

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