> That is not the case. On magnetic drives, the field can spread beyond > the region > written to by the drive heads, and can be read by a suitably equipped > lab. Reports > on how effective this is and what methods can be used to destroy the data vary, > but it's safe (or rather, it's necessary) to assume intelligence > agencies or big > companies can do stuff we don't know about. > > Besides, drives can transparently reassign sectors that go bad, and no mere dd > can get to those. If 'they' can take apart the drive or get suitable > firmware for it, > they can certainly read all the sectors. Even if you assume > overwritten data can > not be recovered, you would still need to wipe these sectors.
Like I said, once the information _has_ been overwritten, it cannot be recovered in any lab. A fellow from IBAS said this during a seminar I attended recently. He even said it was a fundamental principle for all professional data recovery. If it had been possible to retrieve overwritten data from harddisks, im pretty sure the technique would have been used in some high profile criminal investigation. But it hasnt, because it is a myth. And like you said, there are indeed issues to actually performing a complete overwrite. / Dennis
