Perhaps...
I would like to say:
a) Substantial criticism does not make a technical feat impossible. I have seen to much to unsubscribe to the possibility.
b)
When data have been physically overwritten on a hard disk it is generally assumed that the previous data are no longer possible to recover. In 1996, Peter Gutmann, a respected computer scientist,[citation needed] presented a paper that suggested overwritten data could be recovered through the use of Scanning transmission electron microscopy.[1] In 2001, he presented another paper on a similar topic.[2] Substantial criticism has followed, primarily dealing with the lack of any concrete examples of significant amounts of overwritten data being recovered.[3][4] To guard against this type of data recovery, he and Colin Plumb designed the Gutmann method, which is used by several disk scrubbing software packages.
Although Gutmann's theory may be correct, there's no practical evidence that overwritten data can be recovered. Moreover, there are good reasons to think that it cannot.
When I read this I think as follows....
examples of significant amounts of overwritten data being recovered. does not imply that NO data can be recovered, but it clearly states by the same accord that some data can be recovered.
Also keeping this in mind when we discuss computer forensics, you have to take in account that convictions may be rendered out of the court proving the fact it is highly probable that the data previously contained is what the accused is stated to have had on the disk per the claims of a prosecutor, and this has nothing to do with the accuracy of the disk wiping or forensics tools used, but rather the fairness or legal rights system where we often see cases closed with convictions for crimes of association.
In other words, only because the data cannot be recovered to 100% or sometimes even 10 %, it is still up to the court system to make use of the data as they deem fit, and unfortunately they often do in many countries to this date.
In fact, pretty much like any other decent data recovery application, one cannot expect to get all degraded data back all the time.
EDIT:
A word from Mr Gutman himself in regards to MFM methods applied to modern / newer media types with high density and perpendicular clusters...
Gutman said:
“Any modern drive will most likely be a hopeless task, what with ultra-high densities and use of perpendicular recording I don’t see how MFM would even get a usable image, and then the use of EPRML will mean that even if you could magically transfer some sort of image into a file, the ability to decode that to recover the original data would be quite challenging.”
In all fairness, yes I do agree it would seem quite impossible (Today, but perhaps not tomorrow), to do this on newer disks, but given the number of people using older disks for bulk hording and storage it would seem fair to say a majority of the media could in fact be target for the said method, when it is older.
Even so the very good article on this topic found at
http://www.anti-forensics.com/disk-wiping-one-pass-is-enough
and...
http://www.anti-forensics.com/disk-wiping-one-pass-is-enough-part-2-this-time-with-screenshots
...does not negate the possibility but also describes the difficulty in rendering usable data in return on recovering the same.
Now if information I have received in the past have been misleading or wrong then so be it, but it still does not mean technology has not been developed which is yet to become public in this field, and that can stand for the former co workers of mine whom I discussed this topic with long ago.
A final edit:
Defense Security Service said:
Data sanitization
DoD 5220.22-M is sometimes cited as a standard for sanitization to counter data remanence. The NISPOM actually covers the entire field of government-industrial security, of which data sanitization is a very small part (about two paragraphs in a 141 page document).[4] Furthermore, the NISPOM does not actually specify any particular method. Standards for sanitization are left up to the Cognizant Security Authority. The Defense Security Service provides a Clearing and Sanitization Matrix (C&SM) which does specify methods.[5] As of the June 2007 edition of the DSS C&SM, overwriting is no longer acceptable for sanitization of magnetic media; only degaussing or physical destruction is acceptable.
So to spare the kittens and Rollyco, whom I respect greatly in regards to technical matters, I will stay out.
... wonder why.