Mar 11

For decades we’ve been told by security software vendors that to truly delete data from a hard drive, you have to overwrite the data multiple times with different patterns of 0s and 1s.  But now we can file this away with other computer urban legends.

Computer forensics expert Craig Wright and his colleagues ran a scientific study that overwrites hard drive data and then examines the magnetic surfaces with a microscope.  They published their results in Lecture Notes in Computer Science as Overwriting Hard Drive Data: The Great Wiping Controversy.

The study concludes that after a single overwrite of hard drive data, the likelihood of being able to reconstruct a single byte is 0.97 percent.  The odds of recovering multiple sequential bytes of data (such as a password or document) are significantly less and would require exact knowledge of where on the hard drive the sensitive data is located.

This means data-wiping software that overwrites data up to 35 times may make you feel better, but it only wastes your time and money.

A much bigger data security hole is to overwrite all copies of the data that’s to be deleted.  This is not a problem if you are wiping an entire hard drive, but if you are trying to delete a single sensitive document, you have to worry about temp files, shadow copies, backups, file fragments, the Windows swap file, etc.

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Article published on March 11, 2009

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