/ FEATURE
erased. As we have no way to address it, we can never be sure. out with a hammer or an axe. Once you have the platters,
To get around this, SSDs usually come with a built-in erase op- you will see that they are coated with a shiny material. This is
tion that will ensure that everything is properly reset and back the layer that’s sensitive to magnetism and where the data is
to normal. However it’s worth remembering that traditional stored. Simply take a blowtorch from your local DIY store and
techniques will not work well on these devices; something to give the platter the good news. This will vaporize the layer and
bear in mind before you bet the house on a given procedure. ensure that the data is lost forever.
As you can see, erasing a hard disk isn’t as straightforward
/ The Bottom Line: If I had a Hammer as you might first have thought. Although it’s relatively easy to
(or a Blowtorch) destroy data, there is always a slight risk that the data might
At present recovering information from a disk is either easy or not actually have been erased. There really isn’t any way to be
practically impossible. If the user has taken adequate precau- entirely sure either.
tions, it’s very unlikely that someone with standard equipment The simple rule to follow then is this:
will be able to recover anything. However, we have all seen the If the data you’re worried about is really that sensitive, just
movies where, with lots of random key presses and impressive destroy the disk. This is the only way to truly guarantee that
stuff scrolling up the screen, the hero (or heroine) manages the data will not be recovered. /
to recover data that would otherwise have been impossible.
This usually goes with a nice technical term such as Magnetic
If the hard dIsk Is In a
Resonance Imaging.
Well, this is only slightly science fiction and is becoming more
hundred pIeces, there Is
science fact every day. Hard disk technology is not particularly
no way any data Is goIng
accurate. Most people presume that a hard disk writes either a
one or a zero to the platter and then simply reads that informa-
to be recovered
tion back. What actually happens is that charges tend to be
rather less accurate, sometimes overlap, and are hardly ever RefeRences
exactly one or zero. In fact when the information is written to [[1] Ministry for the environment (2006), `Ownership of electrical and
disk the write head only does enough to ensure that when the electronic equipment’. [Online] Available at: -
data is read, it is obvious which number it should be. As men- http://www.mfe.govt.nz/publications/waste/eee-survey-report-
tioned previously, it is then theoretically possible to look at the jan06/html/page3.html [Accessed 17th of June 2009.]
charge on the disk and based on how close to one or zero it is, [2] casey, e. and R. Dunne (2004), Digital evidence and computer
determine what the last value probably was. crime: forensic science, computers and the Internet, Academic Pr.
Depending on whom you ask, this is either a technology [3] Membrey, Peter, Tim Verhoeven and Ralph Angenendt (2009),
that requires vast amounts of resources to put into play or Definitive Guide to centOs, Apress.
something that is becoming standard across forensics labs. [4] Gutmann, Peter (1996), `secure Deletion of Data from Magnetic and
Like the erasure techniques we’ve looked at, there seem to solid-state Memory.’ [Online] Available at: - http://www.cs.auckland.
be a lot of unknowns and no one seems to be sure – or if they ac.nz/gut001/pubs/secure_del.html. [Accessed 19th of June 2009.]
are, they’re keeping quiet about it. At the end of the day, all we [5] Us Department of Defense (2004), `national Industrial security
can do is minimise the chances of data recovery and hope that Program Operating Manual’.[Online] Available at : - http://www.dtic.
if these advanced recovery technologies do exist, they’re not mil/whs/directives/corres/html/522022m.htm [Accessed 19th of
going to be pointed at our data! June 2009.]
As you can see, erasing a disk is not as simple as it might [6] feenberg, Daniel (2004), `can Intelligence Agencies Read
appear. All of the techniques mentioned have their flaws. As Overwritten Data? A response to Gutmann.’ [Online] Available at: -
these techniques get more complicated, the required effort http://www.nber.org/sysadmin/overwritten-data-guttman.html..
and cost to recover the data increases enormously, and in real- [Accessed 19th of June 2009.]
ity it will be extremely difficult for any data to be recovered,
even from a disk that has just been zeroed.
That said, if you are really concerned about the contents of
/ Author Bio
a hard disk, the easiest way to deal with it is to destroy the Peter Membrey lives in Hong Kong and is
hard disk physically. This may sound a bit crazy, but hear me
actively promoting open source in all its
various forms and guises, especially in
out. Presumably, whatever is on the hard disk that you want
education. He had the honor of working
to erase must be highly sensitive. How much damage would
for Red Hat and has received his first
it cause you if it were to fall into the wrong hands? If you now RHce at the tender age of 17. He is now
compare that cost to the price of a new hard disk, suddenly it
a chartered IT Professional and one of
the world’s first professionally registered IcT Technicians.
doesn’t seem so bad. If the hard disk is in a hundred pieces,
currently studying for a master’s degree in IT, he hopes to
there is no way any data is going to be recovered.
study locally and earn a PhD in the not-too-distant future. He
There are various ways to destroy a hard disk. A very effec- lives with his wife sarah and is desperately trying (and sadly
tive way is to remove the platters from inside the drive. You
failing) to come to grips with cantonese.
can either do this with the proper tools, or you can bash them
19
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