I have a broken HDD that contains sensitive data. Since no software can access the disk, I can't wipe it using any of the tools generally suggested.
Breaking the disk physically into very small pieces would probably suffice, but that would require some good tools to do. Just waving a magnet around the disk might still leave the data recoverable by data recovery experts, or am I wrong?
What's an effective way to clear the sensitive data?
You're correct; physical destruction is the only good way to do this (you'd need a magnet so strong that it's not feasible to get one for most people unless you're on staff at the Large Hadron Collider). Professional disposal operations generally do this with an industrial metal shredder. For you, bending the platters with a hammer, sandpapering them, and then running a drill through them in multiple points is sufficient to stop anything but advanced forensic data recovery. If you're really concerned about even that, or you just want style points, you might try thermite. It is usually sufficient to melt the platters entirely.
On newer drives, even the high-power magnets I used to use don't work anymore to erase the disk.
If you have a spike, or similar object (hard metal that is pointed, think of a nail that is much bigger) and drive it through the center of the chassis with a hammer. That will bend the platers and damage the heads making it extremely difficult to recover.
A land stake from the hardware store should work for this.
Dispose of the board separate from the drive. This way any encoding information about the drive recorded on the controller will not be available making recovery exponentially more difficult.
After all that, you can safely send the remains to a computer recycler for shredding.
Apparently the method a certain british university uses is drilling a hole through it. Failing which, thermite.
In addition to all the advice above mentioning physical demolition, I would like to add putting the platters in an oven at the highest possible temperature for ca 20 minutes. IIRC, at those temperatures (if sustained) the magnetic information is lost.
If you think that is insufficient, heat up the platters over an open flame until they more or less glow (gas stoves are great for this!). At that point any information on them is essentially wiped. The flame of a candle could be sufficient, but would require some patience as you "anneal" the surface one square centimeter at a time.
Melting them with termite certainly will destroy the information, but is messy and dangerous and essentially not something you can do at home (in contrast to use a kitchen oven or gas stove).
Edit: Disclaimer: even if using an oven or gas stove is relatively safe from a fire hazard perspective, heating these platters might emit unpleasant and potentially toxic fumes. Make sure you have some good ventilation. Also, what I had mind when writing the above is to just heat the platters themselves, not the entire harddrive with controller card and all. (Disclaimer added as per Shinrai's recommendation).
You could use a Propane Torch to do the job. You can melt the platters with it. Clean job :-)
I opened a lot of drives, and they contain strong neodym magnets inside, so I suspect that trying to erase the data from outside is a waste of time. However, I would like to hear an expert, if just the electronics get destroyed by strong magnetism, or how much energy you need, to erase a hdd from outside.
But most drives have small stickers at the side, which cover small wholes, about as thick as a pencil. You can open the drive, fill it with sand, and turn it around sometimes. Or scratch the surface with a screwdriver or something like that.
I can recommend to open the drive, to get to the magnetic end of the head. Meanwhile, you get to the platters and can scratch them enough, to make it expensive as hell to recover some data.
Here is a step by step guide on how to take apart the drive and then sand the and destroy the platters to surely make the data unreadable.
Also, instead of using the Torx screws, you can use a flat-head to remove the top of the hard drive.
You should take it to a shooting range! What better way to improve your aim, destroy the disk, and have fun while doing all that.
Years ago, you used to be able to smack the center with a ball peen hammer, and this was enough to knock the platters off of the axis, and the minute someone came along and tried to power up the drive, the platters would get shredded internally when it tried to spin. Not sure if this is still a valid tactic or not.
The only way to permanently destory data with no chance of any recovery regardless of how much effort you could put into recovery is to heat the platters to the Curie point. Granted, that's possibly beyond the point at which the platters will turn to molten metal, but for absolute certainty of destruction in a cost-is-no-object scenario I'd feed the disks through a hammer shredder and then melt the results into bars.
It should be pointed out that it doesn't take much distortion of the magnetic signal to make the disks useless. The forensic techniques that used to be effective on a drive are now part of the standard electronics, just to get the densities required. A little sandpaper is probably perfectly effective.
If you want total security, just keep the platters and use them as coasters.
The site http://www.diskstroyer.com/ sells a kit that includes the equipment and directions about how to destroy the drive.
According to wikipedia, sufficient quantities of concentrated hydrofluoric acid will completely dissolve glass, ceramic, and aluminum, the three most common substrates for hard disk platters.
It's not exactly a household item, though.
Call a couple of your local document shredding companies. Most have gotten into the media destruction angle at this stage. Around here (New England) the average cost is about $10/disk for them to drop it into a monster chipper. Itsy bitsy pieces out the other end. If I do this for a client, I usually get a zip-lock baggie of pieces to bring back to them as proof, along with the receipt. I used to use several of the methods above, but for $10, it's not worth the time and effort.
