Digital Forensics Magazine Issue 1

/ FEATURE
DATA ERASURE –
FACT OR FICTION?
Don’t give away your personal data along with your old PC!
by Pete Membrey
/ INTERMEDIATE
W
ith stories of lost USB keys, stolen laptops, and Hard disks aren’t really very intelligent devices, at least
personal data being recovered from second hand not at the operating system level. To the operating system, a
machines, it’s a wonder we’re not too scared to even hard disk appears as a large amount of memory that can hold
touch our computers these days. But how serious is this ones and zeros, nothing more [2]. As there is no predeﬁ ned
risk? Is it really as bad as people seem to be making out? structure, we need to apply one by formatting the disk. How
How easy is it to recover data – and can we prevent this works depends on the ﬁ lesystem, but basically it arranges
“black hats” from doing it? and allocates space in such a way that we can easily store and
We’ve all seen the horror stories in the news about people retrieve our information. There are two key parts to the ﬁ lesys-
recovering information from hardware that they’ve bought tem – the index and the data. The data is the information in a
from eBay. Traditionally researchers would buy desktop and ﬁ le that has been stored on disk. The index provides a quick
laptop computers and try to recover information from them, way for the operating system to ﬁ nd that data. In essence, we
usually with a great deal of success. These cases tend to pick the ﬁ le based on information in the index, which is then
make the news because a researcher managed to ﬁ nd private used to locate the ﬁ le on the disk platters.
photos or credit card information, and that makes for an excit-
ing story. After you read the shocking title, you’ll be treated
IF THE HARD DISK IS IN A
to a long spiel on why if you don’t erase your disks properly,
someone is going to steal your identity, blackmail your wife, HUNDRED PIECES, THERE IS
and post naughty pictures all over the Internet.
NO WAY ANY DATA IS GOING
It’s not just laptops any more either. These people are
buying up anything that could ever store information. Even a TO BE RECOVERED
ten-year-old Nokia mobile phone stores information such as
phone numbers, text messages, and whom you’ve been call- When we delete a ﬁ le what we’re actually doing is remov-
ing recently. Imagine the juicy titbits that can be pulled back ing the entry in the index and telling the ﬁ lesystem that it can
from an iPhone or a netbook. Indeed, practically every digital reuse the space that the ﬁ le has been using. As an analogy,
device on the market stores some sort of personal informa- think of a map of a wilderness that shows a mountain. Now,
tion. Even if you don’t consider your mother’s phone number if we remove the mountain from the map, anyone who looks
very sensitive (though I bet she’d disagree), you still don’t at it will see empty space. But if that person actually looks
want just anyone getting hold of it. at what’s really there, the mountain will be very easy to spot.
This is why deleting a ﬁ le is insecure - it doesn’t remove the
/ Deleting or Formatting versus Erasing data, just the reference to it.
So is there any truth to all this? Well, it is certainly very easy to The same can be said of formatting. Whilst this happens on
recover information from a hard disk if it has not been properly a much bigger scale (across a whole disk or partition), the disk
erased. A simple format is deﬁ nitely not enough – the data itself is not wiped clear. Removing all data on a 500GB hard
can still be easily recovered. The good news is that erasing a disk is not difﬁ cult but it does take a considerable amount of
disk is very straightforward and will prevent all but the most time. So, for performance reasons, a format just creates a new
serious people recovering your data. This is becoming a bigger index and doesn’t touch the data itself.
concern as people buy more and more computers. For ex- Most people when they sell their PC’s, simply reformat the
ample, a government survey in New Zealand showed that the hard disk and reinstall their operating system of choice. This
average household owns 1.2 computers (excluding monitors). will certainly overwrite some of the data, but the operating
[1] This means that the second hand market is likely to be full system will at most take a few gigabytes of space and the
of computer equipment – possibly even yours – that has not previous owner likely used considerably more than that, which
been properly erased. means the data is still there. The new user won’t be able to see
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