[thedoc (OP)]

This week the Naked Scientists go virtual! We'll be hearing how a new computer system can accurately gauge your age from a mugshot, we come face to face with the painting fool, a computer that can read -  and then paint - your emotions, and we find out what's still lurking on your hard disc, even after you think you've wiped it. We also unveil Second Naked Scientists - our home in Second Life - and get stuck into a new molecular glue designed to replaces surgical stitches and staples. Plus, in Kitchen Science, Ben and Dave embark on a far from fruitless mission to charge an MP3 player with an orange...
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If you want to discuss this show, or ask a question, this is the place to do it.

[paul.fr]

In the Computer Forensics part of the show, it seemed (to me)to be implied that erasing your hard drive just once was good enough to prevent people recovering your data. If I heard right, then that is false. You need to erase the drive multiple times to even stand a chance.

I wipe my drives routinely 35 times using the gutman method, this free piece of software is what i use.
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[another_someone]

Deletion of a hard drive does nothing.  It is the overwriting of the hard drive that actually physically removes the data.  There is some talk that one can still detect residual signals from the original data even when new data has been written over it, but I would have thought that even if you could technically detect some residual signal, trying to seperate the residual signal from the new data that you have overwritten it with would be next to impossible.

The bigger risk is if overwriting the data does not overwrite every track of the original data (e.g. if some of the original data has been subsequently marked as a bad track, and prohibits you from writing over it, but still allowing somebody who can bypass the electronics of the drive to read most of the original track).

Nonetheless, the only people likely to be doing this are going to have very specialist equipment, and if you are not doing anything criminal, and are not managing particularly sensitive data, then few people with that level of sophistication of equipment are likely to be that concerned about what you have on your hard drive.  This is not to say that you should not be careful about the data, only that the degree of care has to take into account just how much effort it is worthwhile for others to undertake to obtain the data from your drive.

[paul.fr]

Deletion of a hard drive does nothing.  It is the overwriting of the hard drive that actually physically removes the data. 

Which is what the above programme does. Overwriting, erasing...tomato, tomato

[BenV]

Graham and I did discuss the chance that data could be recovered after just one overwrite, due to a 'magnetic resonance' effect which may indicate what position each bit had previously been in.  Sadly, we had to remove this from the interview due to time constraints.

One overwrite will stop the vast majority of people from retrieving data with easily available software, but the determined could get something out of it.  Apparently with early hard drives they recommended wiping 32 times, but with modern discs you shouldn't need more than 6-7 wipes.

[chris]

Blimey, that's a shock. Thanks for that bombshell Ben; I'd never have believed it.

Chris