For decades I have heard about HDs needing to be overwritten several times before being discarded. All to avoid someone from being able to retrieve information from that HD. It seems that we have been a little too paranoid. At least that is what Craig Wright, Dave Kleiman, and Shyaam Sundhar three forensic experts say in a White Paper they published.
According to the White Paper the chance of getting a Bit back the correct way is only 56% (which is close to flipping a coin). As a result the chance to reconstruct a Byte correctly is only 0.97%! You can imagine how this looks like for even a file in the Kilobyte range.
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