Overwitten data: Why even the Secret Service can't get it back

Ontrack Data Recovery said so. Now KÜRT offers a second opinion: Deleted files may be recoverable, but file data that's overwritten on a modern hard disk is dead. Period. Even the most advanced techniques used at the Secret Service won't get it back. So says Dea Franko Csuba, marketing director at data recovery specialist  KÜRT Corp (which also goes by  the name KUERT outside of the company's home base in Hungary).

In my recent story, Surviving a home data disaster: How Shirley got her files back, Ontrack tech Sean Barry was quoted as saying that it's no longer possible to recover data from an overwritten area of a disk. Some readers challenged that, so I asked Barry to respond. He did so here. But one reader claimed that other recovery specialists, such as those at KÜRT, could indeed resurrect overwritten data. So I asked Csuba if KÜRT could do any better.

Csuba's response:

"The overwriting of data renders it irrecoverable even by a world-class data recovery firm such as KÜRT. This is because, as a result of the overwriting, the existing magnetic structure is replaced by the magnetic structure of the new data. In other words the magnetic dipoles on the surface of the disc are rearranged in accordance with the new data. It is obvious that a given magnetic dipole can only assume one polarity at a time, and as a result its overwritten state can under no circumstances preserve its previous state.

Approximately 20 years ago, in the era of hard discs using MFM (Modified Frequency Modulation) and RLL (Run Length Limited) technologies, there was a theoretical (!) possibility of identifying the remains of overwritten data, owing to slight inaccuracies in the head control and movement. From the magnetic traces that could arise from this imprecision, it was alleged that highly secret, extremely high tech and - of course - incredibly expensive Secret Service techniques could possibly be used to recover some of the data.

This possibility, if it really did exist, was far beyond the competence of even the leading data recovery firms. Today’s data recording technologies virtually preclude the possibility of such data traces being left behind. The head control mechanisms have now been perfected to the stage where this method could not work."

Copyright © 2007 IDG Communications, Inc.

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