
Can I erase sensitive data on an old hard drive with Neodymium Magnets? - artbristol
https://www.kjmagnetics.com/blog.asp?p=hard-drive-destruction
======
EvanAnderson
Here's my anecdote: In 2006, while sitting at my desk playing a video on the
hard disk drive of my Thinkpad T22, I held a single neodymium magnet
(harvested from an old hard disk drive) about 6 inches from the left side of
the unit (where the ~40GB-ish Travelstar 2.5" PATA disk was located). The
video froze, Windows XP blue-screened, and the hard disk drive started
emitting a ~10Khz whine. I jerked my hand away from the PC immediately when
the whine started.

BIOS would no longer detect the disk on that machine, or any other I tried it
on (on both USB-to-PATA and honest-to-goodness motherboard PATA controllers).
The drive spun up but made a repeated ticking sound (I assume seeking back and
forth looking for servo tracks).

I sent the drive to Kroll Ontrack (because, stupidly, I had billing data that
wasn't backed-up on the drive). The report I received back indicated that 80%
of the drive's sectors were unreadable.

As an aside: The data I was looking for was ASCII text and Kroll Ontrack was
completely unhelpful in just sending me a bitstream image of the drive so I
could grovel thru looking for data I needed. Being plain ASCII, their "file
carving" tools didn't locate any of the data. (They sent me a "preview" of the
data they'd located, and while it got lots of Microsoft Office-format files,
it didn't have any ASCII text files). I offered them a 3x multiple of the rate
they asked for file-level recovery to simply send me the bitstream image of
the disk that they'd already made. They wouldn't do it, and wouldn't even let
me pay to talk to somebody who understood what I was saying. I ended up taking
a major loss on the billing data I destroyed. I'll never recommend them to
anybody.

I won't ever play with neodymium magnets around spinning rust media again.

~~~
dpedu
From 6 inches away? Unless this was a hockey-puck sized magnet I'm calling it
a coincidence.

> (harvested from an old hard disk drive)

Okay, this is making even less sense. "Hard drive magnets", in a drive, are
millimeters from the spinning platters. I refuse to believe that the same
magnet, moved 6 inches _away_ from the computer caused catastrophic damage.

~~~
EvanAnderson
I will definitely concede that the 6" number may be an incorrect memory. It
certainly may have been closer, but it wasn't right on top of the unit.

If it was a coincidence it was certainly well-timed. I don't have the Thinkpad
anymore, but I do still have some 2.5" PATA drives. It might be interesting to
test this and make a video.

Here's a picture of the magnet in question (it holds stuff to my refrigerator
now), w/ a penny for scale:
[http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg](http://mx02.wellbury.com/misc/20171203-Magnet_of_doom.jpg)

This magnet was pulled from a Micropolis 9GB SCA-II 3.5" low-profile drive
dating from roughly 1998 (I had a crap-ton of these drives and, as they died,
I pulled their magnets, so I have a bunch of these). These particular magnets
will stick to each other thru my 3" thick butcher block table. They are
physically larger (substantially thicker) than the ones I've pulled from newer
drives.

Edit:

I assume that the data and servo tracks written to the drive are done so in
the presence of the magnetic flux of the magnets supporting the voice coil. I
always just assumed that adding a substantial new source of magnetic flux (the
magnet in my hand) either induced a current or magnetized some component in
the drive.

~~~
syshum
>> They are physically larger (substantially thicker) than the ones I've
pulled from newer drives.

Not really, they look very close in size to current Enterprise Drives
([https://imgur.com/2HjuuKM](https://imgur.com/2HjuuKM)), Of course I have
removed the Metal backing plate from mine

Now consumer drives do have smaller magnets (that is one way to save cost)

Here is a photo of the 4 styles of magnets I still personally have, the
smaller magnets are either out of consumer drives and 2.5in drives
manufactured in the last 7 years
[https://imgur.com/59XjVPm](https://imgur.com/59XjVPm)

And just for fun a small assortment of my collection because why not

[https://imgur.com/bW6ycRI](https://imgur.com/bW6ycRI)

~~~
EvanAnderson
I've only had the opportunity to tear down a few consumer drives in the last
few years. I haven't seen inside an enterprise-class drive in a few years.
(I've stopped dealing with hardware directly for my Customers, and I haven't
purchased much hardware for personal use over the last few years.)

I've found scavenged hard drive magnets to be very useful for odd jobs. One
served several years holding up the fallen head-liner over the drivers seat in
one of my crappier cars.

------
tscs37
If you want to get rid of a harddrive with sensitive data I would first
suggest that one gets familiar with the thought of not being able to sell it
as used.

Personally for my drives, I use Boot and Nuke to erase the drive three times,
first with zeroes, then with random data, then with zeroes again. After that I
disassemble the drive, put a strong magnet over each platter, shredder the
drive into almost powder, burn the pieces in a fire and then throw away the
leftovers. Probably overkill but I want to be certain.

~~~
readams
Normally you'd want to throw the remains into a volcano but I guess if you
feel safe just throwing it away then you do you.

~~~
Spooky23
You jest, but jackass security people would probably be dissatisfied that your
PII might be accessible to some alien race when after the earth explodes in 5
billion years and some remanent of data is somehow recoverable from an
asteroid made of cooled lava.

I recall one datacenter consolidation project where the hard drives from
decommissioned servers were zapped with a degaussing device, shredded, and
then somebody signed off that they were dumped in a furnace somewhere. (At
some ridiculous expense)

Meanwhile, the normal operation bins of drives that were in little blue bins
for collection where just picked up and moved by the moving men, and are
probably still in some closet in the new facility!

~~~
PuffinBlue
I failed an audit once because the inspection team managed to recover data
from the information encoded on the event horizon of a nearby black hole.

Can't be too careful nowadays.

~~~
QAPereo
Another good worker screwed by the holographic principle.

Edit: wow... that joke went badly.

------
Lramseyer
I worked in the HDD industry, doing signal processing for a few years. HDDs
are pretty much magical. It's insane how delicate, yet robust it all is.

But to put things into perspective with some numbers, the write heads on a
modern HDD use somewhere on the order of 50 mA of current. That may sound like
a reasonable amount until you consider that the magnetic field [flux] is
condensed down to a 60 x 20 nm area. It usually takes a little over 1 Tesla to
flip the magnet.

I have been out of the Industry for a little bit now, but things are moving
towards a magnetic substrate that has a smaller grain size (allowing smaller
bits at a similar SNR) but a coercivity well over 3T at room temperature.

~~~
zkms
> HDDs are pretty much magical. It's insane how delicate, yet robust it all
> is.

Absolutely. It's bloody amazing how my laptop has a device with finger-sized
actuators that read/write bit cells that are about as small as couple-year-old
semiconductor feature sizes -- and that can survive mistreatment that one
doesn't usually associate with micromanipulators.

------
magnat
Hard disks are surprisingly hard to destroy on-demand. There was a DEF CON 23
talk [1] exploring ways to quickly wipe your servers in situ using physical
methods.

[1]
[https://www.youtube.com/watch?v=-bpX8YvNg6Y](https://www.youtube.com/watch?v=-bpX8YvNg6Y)

~~~
FRex
I instantly though it was this (hilarious) one instead:
[https://www.youtube.com/watch?v=1M73USsXHdc](https://www.youtube.com/watch?v=1M73USsXHdc)

~~~
jacquesm
They should have used a plasma torch. Legal, relatively easy to contain too
(just put a water bed below it).

------
snvzz
Just encrypt each and every one of your drives.

It makes their end of life that much easier.

------
cmurf
I think magnets could compromise the read/write head, or other electronic on
the drive. So why not just mulch the drive with a grinding service?

If you're looking to reuse the drive, use one of the NIST SP 800-88 Revision 1
recommendations. It lists the methods in the preferred order. Ideally the
drive supports ATA crypto secure erase, where it just wipes the DEK and KEK,
poof, in effect the crypto encoded form of you data can no longer be turned
into plain text. You can mimic this with software FDE (Bitlocker, LUKS/dm-
crypt, Filevault). Fast.

But they also say it's adequate to use the other kinds of secure erase,
because other than firmware bugs/exploits it's the only way to erase sectors
not assigned an LBA, e.g. sectors that once had an LBA, had data written to
them, but subsequently failed overwrite and the LBA remapped to a reserve
sector, leaving data on a sector that cannot be overwritten via SATA commands.

------
FRex
Here are few experiments with a 6 inch neodymium magnet with few devices:

[https://www.youtube.com/watch?v=_yEu2R1gYSs](https://www.youtube.com/watch?v=_yEu2R1gYSs)

[https://www.youtube.com/watch?v=4l-6qWaZpVQ](https://www.youtube.com/watch?v=4l-6qWaZpVQ)

------
OliverJones
HIPAA - regulated health data requires physical destruction of retired hard
drives. Usually this is done in sight of a video camera. The operator shows
the drive's serial number to the camera and then drops it into the grinder.

CMS (Centers for Medicare and Medicaid Services) can require proof of
destruction. That video does it.

~~~
rasz
so secure, guess nobody heard of $100 label printers

------
nixpulvis
This is exactly how I got out of a final project in middle school. Wiped my
HDD with a Neodymium magnet right before the deadline and claimed my computer
was "broken"... Of course this wasn't done for highly paranoid reasons where I
needed to ensure the data was _really_ all gone, but funny story nonetheless.
People are more sympathetic when they think a computer "randomly" stopped
working.

~~~
keithpeter
Alas, such a strategy will not work at universities local to me (UK). They
_specifically_ exclude computer malfunction as grounds for extenuating
circumstances.

~~~
nixpulvis
This was back in like 2005 or something too...

------
KaiserPro
Thermite, both fun _and_ effective.

~~~
RyJones
My old Yubikey was in between layers of explosives here:
[https://youtu.be/XYOZEPr3Jzw](https://youtu.be/XYOZEPr3Jzw)

------
dboreham
No. You need to cast it into the fires of Mordor. Or something similar.

~~~
gruturo
Something similar is indeed the right answer here. You have to take the
material above its curie temperature
([https://en.m.wikipedia.org/wiki/Curie_temperature](https://en.m.wikipedia.org/wiki/Curie_temperature))
and then according to physics all preexisting magnetic information is lost.

------
oldandtired
There are techniques used to recover previously erased information on HDDs.
These techniques have been available since the 90's. The best way to make it
unrecoverable is to melt the disks by the use of whatever techniques you have
available, including ox-acetylene torches (the favoured method for the company
at the time I was working for them), putting into a furnace (as suggest by
others here), etc.

The problem with erasure is that there is residual amounts of magnetic fields
that can be picked up by the right equipment. In the day, it was reported that
they had success with recovery of information that had been overwritten by 8 -
10 times. It just took a lot of patience to do so. Those who want to recover
this information will have that patience.

~~~
rasz
These techniques are theoretical from the time HDDs needed a user low level
format(think RLL controller in your XT), and even then a myth nobody ever
demonstrated in practice.

------
mark-r
Is it really necessary to overwrite the data multiple times to erase it? With
the densities provided by today's hard drives, the techniques you used to be
able to use to get partially erased data are routinely used by the disk drive
itself for normal reads.

~~~
FooHentai
What's your threat model? Data must not be recoverable for at least the next X
years, or data must not be recoverable within any future time frame, no
exceptions?

For the former, you're absolutely right. For the latter, multiple-pass
overwrite provides greater assurance than single pass. Following that up with
physical destruction of the platters provides further assurance.

~~~
KozmoNau7
Why even bother with overwriting the data if you're just going to physically
destroy the platters and/or heat them beyond their curie point anyway?

~~~
FooHentai
Timeliness, usually. Destruction is usually a batch job so if you care about
risk of data exposure in the time lag between being able to wipe the drive
(usually an online, relatively low-hassle activity) and destroying the drive,
wiping is worthwhile.

Again, thread modelling is crucial. There may be no point wiping!

------
richev
When I had a few old hard drives to dispose of I drilled several holes in each
one, through the case and platters, then filled them with water and left them
outside for a few days so that anything that might rust would do so.

------
wheresmyusern
even if you drill a hole in the drive, data can still be recovered from it.
anything that leaves large pieces of drive intact really isnt ideal. over the
years i had collected dozens of platters from both myself and other people.
for some reason, when i was younger i was obsessed with collecting hard drive
magnets and also smart enough to understand that i probably shouldnt throw the
platters away. so a few years ago i decided it was time to destroy all of
these annoying platters that i have to worry about misplacing. i naturally
assumed that it was going to be easy to find some kind of service, shredding
or wiping, for hard drives or hard drive platters. there were no good options.
so i tried smashing the platters into small pieces, and this worked for some
of the thinner laptop hdd platters. one strong hit would break them into
millions of tiny pieces. but most of them just bent or dented. and to
thoroughly bend and dent the whole surface of all the platters would be super
annoying. so i decided i should just melt them -- they are made of aluminum
which has a low melting point. it was surprisingly easy. just get an old
coffee can or better yet a stainless steel gas cylinder or even a ceramic
crucible. they arent too expensive as far as i know. i used a can. then just
surround the can with some bricks for insulation and apply a normal blow
torch. set the torch down so it blows into the void between your vessel and
the brick jacket. after the platters are melted you can even cast them into
something, like a belt buckle. its all a bit silly, but it does feel nice to
know that it is literally impossible for anyone to ever know what was on those
platters.

~~~
kosma
You don't even need to melt them. Just reaching the Curie point should be
enough.

------
tinus_hn
Even if the test would have succeeded, this is a bad idea.

With a magnetic swipe card that you demagnetize so it is no longer read
successfully, you may well be able to recover the information using a better
reader.

Depending on drive age the same may be possible using a hard drive.

The best option for modern drives is still to use software to wipe the drive
and if reuse is not required destroy the reading mechanism and platters.

~~~
Filligree
I won't say it's completely impossible, but modern HDD read heads are already
close to our technical limit, and the signal they get is so noisy as to
require extensive processing.

There definitely was a period where labs could recover data this way, but I
think it's passed.

~~~
Johnny555
Hard drives automatically remap bad sectors, so even if you overwrite 100% of
the accessible data, you may still have left pieces of data in remapped
sectors that weren't overwritten. If your drive supports the SECURITY ERASE
feature, then it should overwrite those blocks too.

Though if you really want to sell or give your drive to someone else, the best
thing to do is to use full disk encryption from the beginning, then there will
be no plain text data on the drive.

------
golem14
For quickly destroying hard drives, drive big nails through the entire case in
several places. Restoration is at least very manual and annoying, in many
cases not worth the effort.

If you need more security, building a simple furnace isn't too hard:

[http://eecue.com/c/driveslag](http://eecue.com/c/driveslag)

~~~
mirimir
You don't need to go that fancy. Just use a small steel drum, with holes
punched around the bottom, sitting on bricks. Burn dry hardwood, plus
occasional chunks of paraffin. Everything burns off, except for the steel.

------
tfha
Best method is to use LUKs and then wipe the master key. Luks has a forensic
stretching technique to take a 32 byte master key and stretch it to 1 MiB,
such that loss of a single bit means the original key is unrecoverable.

That really helps you wipe things like SSDs which can copy and migrate data,
and make it hard to be certain you destroyed a sector

~~~
darkmighty
> such that loss of a single bit means the original key is unrecoverable

That can't be right (I don't know anything about this though). If you control
the data (with a non-interactive non-destructive decryption process), a loss
of a single bit just means you have to test two possible keys. In terms of
brute forcing, the security is the same per number of bits lost. The benefit
of using a large key would be that if you lose a certain _fraction_ of your
key (say 10%), then that would correspond to more bits (as long as you erase
128 or more bits you'd be fine).

Also beware of key stretching, use it only when absolutely necessary. Key
stretching doesn't modify the ratio of work necessary for your
encryption/decryption vs the work necessary for brute forcing -- i.e. it
doesn't improve the security factor. You're essentially doing an economic
defense vs a mathematical one, and hoping that computers won't improve and
your attacker isn't willing to spend much relative to what you spent.

------
nilram
A friend uses a saws-all (or something of that ilk) and cuts them in half. I'm
figuring on taking my old drives to him for that treatment. I don't want to
resell them and have a casual snooper recover my data, and I'm not of enough
interest for anyone to piece the halves together.

~~~
Symbiote
What's the risk from simply writing over the drives with zeros, and sticking
them in the electronics recycling?

I don't think anything I or my employer has would be worth the effort to
recover.

~~~
topspin
This is what NIST says about it[1]:

    
    
        Advancing technology has created a situation that has altered previously held best practices
        regarding magnetic disk type storage media. Basically the change in track density and the
        related changes in the storage medium have created a situation where the acts of clearing and
        purging the media have converged. That is, for ATA disk drives manufactured after 2001
        (over 15 GB) clearing by overwriting the media once is adequate to protect the media from
        both keyboard and laboratory attack.
    

That's an elaborate way of saying that zeroing a healthy modern disk is
sufficient. No need to break out the crucible or jackhammers. If you _really_
need to indulge your paranoia then use some wiping system that does multiple
overwrites with random data. It's not necessary, but at least you won't put
your eye out.

[1]
[http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublic...](http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-88.pdf)

If the device isn't healthy and can't zero all of the media then you will need
to resort to physical destruction.

~~~
abrookewood
Yep. You can over write it once with zeroes (or random) and you are done.

------
amluto
A ferromagnetic cage such as a hard drive enclosure can shield against
magnetic fields pretty well. The field lines are concentrated in the enclosure
and mostly avoid the inside. I would imagine you need to open the drive up to
have much effect.

~~~
jimmyswimmy
TFA said specifically that they could tell that the larger magnets were
imposing a field inside the drive itself, and they could tell it was so
because they could hear sounds coming from inside the drive. They presumed
that the sounds were generated by deflection of the discs under the magnetic
field. Therefore it is evident that the field is penetrating through the outer
case.

They surmise that it was the higher coercive ty of modern drive plates that
causes them to be resistive to reprogramming bits with a static magnetic
field.

------
cptskippy
I normally unsubscribe from junk mail and advertising from e-commerce sites,
KJ Magnetics is one of the few exceptions. I always look forward to their
emails and blog entries.

------
X86BSD
I think I’d rather store the data on a gbde encrypted disk and simply toss it
when I’m done. Then I know the data can’t be read.

------
rodgerd
An angle grinder through the drive, repeatedly, may or may not be the most
effective mechanism, but the sparks sure are pretty.

------
codewritinfool
take it apart, screw the platters to railroad ties. use belt sander on
platter. flip the platters over. repeat. burn sandpaper.

take a hammer to platters to seriously deform them and throw them in the
trash.

not recoverable, imo.

------
coretx
Microwave ovens do wonders.

------
JTechno
HDD's are shielded with mu-metal: [https://en.wikipedia.org/wiki/Mu-
metal](https://en.wikipedia.org/wiki/Mu-metal)

