Edward,Edward said:I used the Western Digital utility to write zeros to the drive. Is
that enough? Should I do it more than once?
Is there a freeware utility I can use?
Jan said:I have heard claims of doing it more than 3 times. If you have Linux:
dd if=/dev/zero of=/dev/your-harddisks-device-name block=1024
count=size-of-disk-in-kilobytes
Why should it be done more times than once? If byte is once written as
zero, isn't it zero, then?
Well, if you do it more than once, that's because you really mean it!
Michael said:Well, if you do it more than once, that's because you really mean it!
Why should it be done more times than once? If byte is once written as
zero, isn't it zero, then?
Well, if you do it more than once, that's because you really mean it!
De Moni said:Why should it be done more times than once? If byte is once written as
zero, isn't it zero, then?
Arno Wagner said:There are rumours that the old data could be recoverd by some
super-secret process nobody has ever heard about. For mots practical
purposes and a modern disk, once is enough.
It is not for floppy disk or tape.
Flame wars break out over this topic. Depending on the technical
means available, it has been claimed there are (very expensive
and "proprietary") ways to access magnetic domains that have been
"overwritten" - i.e. reduced in strength so that the read head and its
electronics don't "see" it in favor of the new data, but which are still
there - either just outside the normal magnetic track or beneath it or
oriented at an unreadable angle. These older domains eventually sink
into the magnatice noise as newer data overwrites and blends the earlier
data into progressively weaker and then indistinguishable random bits.
It is claimed that writing random data (i.e. non-repetitive and unpredictable
patterns) "several" to "many" times over the old data works to hide the
residual old data from sophisticated retrieval procedures that could
otherwise read it.
The bottom line is that if you have data that is sensitive enough for
someone to go to all the trouble and expense of putting your hard drive
through such forensic analysis, you'd best just destroy the hard drive
physically. A session with a sledge hammer and ten minutes on a
charcoal fire should do the job nicely. Oh what the hell, you might as
well set the hard drive on top of a power transformer for a day, too.
Arno Wagner said:Actually, phycical destruction has problems too. The only really
relaible way is to heat up the platters until they loose magnetization.
Also the attacker in this case will know that somebody tried hard
to erase the drive and that trying to recover it might be worthwhile.
For best results, do one (one!) complete overwrite
with zeros and then do physical destruction.
Much more reliable to melt it completely.
No point in writing zeros if you physically destroy it properly.
Previously Alexander Grigoriev said:Magnetic coating in modern drives is only thick enough to hold one domain...
There is no information underneath, as soon as it's overwritten.
By the way, a transformer is not strong enough to erase the data. In fact,
regular black ferrite magnet (used in speakers) which gives stronger
magnetic field than a transformer, is not able to erase even 1.2M 5"
floppies (it could do 360K ones). HDD coating now is much stronger.
Magnetic coating in modern drives is only thick enough to hold one
domain... There is no information underneath, as soon as it's
overwritten.
But not easy, cheap
or safe....
True. But people use unreliable things like drilling holes, sledge-hammers,
degaussers, etc. So at least do one destruction right...
True of your approach too.
And that in spades with the safety of the data.
Huh?
Or realise that zero writing is all you need to do.
The only time that isnt viable is when the drive has died.
Recovery of "erased" data is discussed here:
Secure Deletion of Data from Magnetic and Solid-State Memory
Peter Gutman
http://wipe.sourceforge.net/secure_del.html
Huh?
I advised a single overewrite with zeros.
The "heating up of the platters" is really
reliable in a strong, "absolute truth" sense,
but as good as nobody needs that. Overwriting is enough
for all situations, except when a resourceful attacker knows
that something really, really valuable is on the drive. As in
"your spy-plane is about to emergency land in China".
Huh?
However people manage to get the zero writing wrong all the time.
For example, many think that the "format button in Windows" does
zero wrting and never stop to wonder how it can do this so fast....