It is essential to remove your private data from the hard drive before disposing of a computer, as there are programs that can bring deleted data back from the dead

Scrubbing brush and hard discFollowing on from last week’s blog, that looked at protecting your data by retaining the drive, how do you clean your data off a drive so that the machine is still usable by someone else but without them being able to access your data?

If you always store your data in the locations recommended by Windows and by your programs, then all of your data will be in folders (or sub-folders of those folders) that belong to the signed-in user. Deleting the data for that user is simply a matter of removing that user.

Since there must always be at least one user this means that you need to create a new user (with administrative rights), log into that new user, and then delete the user(s) whose data you wish to remove. The precise method of doing this varies by operating system, but in Windows you need to go into the “Control Panel” and then “User Accounts”. For goodness sake, please ensure that you are satisfied that you have backup copies of anything important before doing this.

If you do not always store your data in the recommended places then there may be other data dotted around the drive that will not be removed by this process. There is no automatic process whereby you can click a button to remove all of this: you just have to hunt around the drive for it and delete it manually using Windows Explorer (or “File Explorer” as it is now known). This can be made a bit easier by using the “search” option in Windows to look for the most common types of data that may be present. Some of these are:

doc – Word documents before Office 2007
docx – Word documents from Ofice 2007 onwards
xls – Excel spreadsheets before Office 2007
xlsx – Excel spreadsheets from Office 2007 onwards
pst – Outlook data file
jpg – image files
tif – image files
pdf – Adobe protable document files
mp3 – compressed music files

However, even when you have deleted the files they are still physically present on the drive.

Eraser logoThe only thing that “deleting” does is to inform Windows that it can re-use the space occupied by the file. So, to obliterate the files, we need to run a special program that over-writes deleted files with random (or, at least, pseudo-random) data. Just in case you are even more pedantic than I am, I should just mention here that a simple, one-pass, over-write could just possibly be reversed. In other words, it’s possible in theory that a single pass will not completely obliterate your data. However, let’s assume that you’re not so paranoid that you think that the CIA or someone is after your data. In that case, a single pass of the simplest form of over-write will probably do.

There are many programs out there that will “scrub” your drive in this way, such as:

  • Eraser
  • Ccleaner – this is an excellent program for removing lots of the temporary files and rubbish that accumulate on a Windows computer. It includes an option for wiping free space clean

Note that it can take quite a long time for these programs to work their way right through a drive. If you were to ask me to ensure that your drive is clean before disposing of your computer I would carry out the above steps, probably leaving you (or ending the remote control session) after starting the “wipe” process as it’s very reliable and wouldn’t need any overseeing by me (or by you, for that matter).

Quite often, my computer support clients are a bit nonplussed as to why “deleting” files doesn’t just do what it says.

Ccleaner logoThe answer is “efficiency”. I like to explain it by using an analogy. Remember VHS recorders and tapes? When you have finished watching the contents of a tape you might very well strike out the contents of the label. This tells you that you have watched the tape and can re-use it. In your mind, you would think of that tape as “having nothing on it”. However, you haven’t actually deleted the contents: you’ve just given yourself a reminder (by striking through the label) that the tape is available for re-use.

Imagine how tedious it would be if you had to go through a lengthy “delete” process that wipes the tape clean before you could record something else onto it. This is exactly how digital computer files are over-written and that is why lots of your old “deleted” stuff might still be on your drive long after you thought you’d sent it to data heaven. This way of doing things is far more efficient during your ownership, and only becomes a consideration when it’s time to dispose of the computer.

By the way, exactly the same situation exists when disposing of mobile phones. I seem to to remember a bit of a fuss fairly recently when it transpired that some mobiles’ options to “restore to factory condition” don’t actually over-write existing data – they just re-install the operating system so that the phone looks as if it’s brand new. In case of doubt when disposing of a mobile phone, I would recommend taking it to your telecomms provider’s shop and asking them for advice.

© 2011-2019 David Leonard
Computer Support in London
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