Magnet to erase Hard drive. Might as well use a hammer
[QUOTE=Sneaknfreak;1877746]A magnet from an old speaker is more than adequate.[/QUOTE]To erase a drive you need a high frequency AC magnetic field. Bringing a powerful magnet close to a drive will "corrupt" the data as the individual flux lines will change certain bits. The drive may be unreadable, but can be reformatted and possibly repaired. A hammer is a better erase device.
And I know of where I speak. A few years ago I had the opportunity to acquire the magnet out of an IBM 370 Hard drive unit (circa 1980). This was one of the 18".6 platter drives with a linear motor. The linear motor magnet actually weighs twenty pounds and is about 8X8X4 inches. A real beast. As a test I placed a VHS tape close. Still played. I then put the tape on top of the magnet and let it sit. It still played. I then investigated how magnetic tape, and subsequently hard drives and computer media worked. And what it takes to erase them. High frequency, or rewriting the bits.
He's what you really need to do if you intend to destroy the Hard Drive vs. Re-use.
What you need to do is destroy the platter itself. As long as that platter is around it CAN be forensically decoded by a motivated / determined entity. Therefore complete platter destruction is most definitely preferred.
Platters are made of extremely hard metal alloy making the hammer method useless. All a hammer does is break the components of the hard drive AROUND the platter, possibly but not likely, leaving any real marks on it. It (the platter) can always be re-installed in different housing with a working "reader" to allow it to be read.
Erasers, can be effective, but work on the principle of over-writing the data with any number of layers of random patterns 1s and 0s. Data forensics have been known to be able to retrieve data even through all those layers.
As mentioned it would take one '7734' of a magnet to affect the magnetic field on the drive. How many people have access to one of these Uber-Magnets anyway? And the results can be dubious at best?
Yes, drilling of holes in the platter can help but there will still be portions of the platter left and who can tell if the holes drilled are in the places on the platter where the sensitive data is?
This is why one should dismantle the hard drive and physically destroy the platter itself.
Now is when a welding torch, preferably a "plasma cutter", can come in very handy. If you know someone who is a welder or mechanic. Someone who has a torch capable of extremely high heat. All that needs to be done is to insert the platter into a vise (after you've taken your frustrations out on it with at least an eight pound sledge hammer.) and melt it into oblivious ashes with that torch. Just be sure you either do this yourself or WITNESS it being done and you'll have nothing to worry about because it's pretty hard to "read" ASHES!