Erasing your data securely

A friend asked what to do to securely erase files when giving their computer to a charity and this is the response I came up with, if you have any suggestions for better software please let me know!

When you delete files on your computer they don't just vanish into thin air, the 1s and 0s that make up the file still remain and these can be retrieved fairly easily (think of all those lovely file recovery programs). Even when a file is overwritten there is still a 'shadow' of the data left behind, this is because of the magnetic nature of hard disks (think of aligning iron filings with a magnet, most will align but not all, and the ones that aren't aligned represent this data shadow).

To properly delete files you can use something like Eraser which can securely erase files you choose. The recommendation is to repeat the process a number of times (3-7) which Eraser supports. However this will only remove the files that you are aware of and things like email and associated settings tend to be hidden away and thus wouldn't be removed. With a bit of work you could probably also remove the email and associated settings but it wouldn't be desperately simple. The Eraser forum has a few posts on how to do this if you don't want to go for the ultimate solution...

The ultimate solution (without destroying the hard disk and putting a new one in) is to do a low level format of the disk a number of times then reinstall everything. This may be overkill but it depends on how important the data to erase is. To do the ultimate wipe (remember, this will wipe windows, all software and all data on the disk and will require a full reinstall of windows/any other software required so you will need a recovery disk and any installation disks you need to put software back on) you would need to download something likeDarik's Boot and Nuke, burn it to CD, put it in the PC, boot up and run the software then when it is finished put in the recovery disk that came with the PC and do a fresh install. Please remember to backup any important data before doing this and be aware that everything will be totally removed so please use with caution! If in doubt, ask your computer literate friend (I know you have one).

If you are doing this for a charity, check with the charity and see if they offer any services regarding data security, they may well do because they will want to set the PC up in a particular way anyway.