It all depends on the level of security required for the information that
is/was on the hard drive.

For most applications, overwriting the drive with a deletion program that
meets the DoD specifications would be sufficient. Merely formatting or
deleting is not sufficient if any of the data is personal or proprietary.

Driving a nail through the platters or shooting the drive, while
delightfully cathartic, is only one step above formatting. It is perhaps
less effective than using a purpose made deletion program. It's good enough
to prevent any casual interest in recovering data on the drive, that's for
sure. However, if the data is sensitive enough to warrant the cost of
recovery, any data on areas of the disk not physically destroyed by the
nail / bullet can be recovered.

Recovering data that's merely deleted (but not overwritten) is pretty
trivial - many programs exist for this very purpose. Data on the drive has
a pointer or address in the file allocation table - basically, an index.
Deletion merely removes the pointer and lets the operating system know that
the space is available for use. The data is still there until it gets
overwritten.

Even once it's overwritten, it can still potentially be recovered, but at a
much greater cost and effort. When the drive heads write data, the
positioning is not exact, and traces of the old data may still exist at the
"edge of the track". This can be recovered in a laboratory situation, with
the proper equipment. This is beyond the means of most, but if you have a
million dollars worth of info on a drive, spending a few thousand on
recovering it can be a good return.

Deletion program are a good step in preparing drives for disposal, if they
are not to be physically destroyed. They are designed to write in at least
three passes - all zeros, all ones, and then random data. This is designed
to defeat the more expensive laboratory recovery methods, and to make sure
that all previously existing data is overwritten. This can take a while,
however, as it essentially involves writing a file as large as the disk
drive on each pass.

If you can physically totally destroy the drive platters, such as by
shredding or melting, that pretty much takes care of all the recovery
options. I've seen recommendations to open up the drive and sand platters,
and that might do the trick on an individual dive, but doesn't seem
workable if you are disposing of more than a very few drives.

Michael Edwards
Blank & Associates P.S.

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