After a US spy plane was forced to land in China and the plane’s disks gave up military secrets, researchers worked to figure out how to quickly and securely erase the disk. Even when the people snooping it had unlimited time and money. Crushing, drilling or explosives would not do the job as fast and as safely as scientists hoped.
According to Dark Reading this proved possible only with permanent magnets – and not the kind decorating your refrigerator.
To create a magnetic field strong enough to penetrate the metal housing around a disk drive and erase the magnetic media inside, the researchers designed a neodymium iron-boron magnet with special pole pieces made of esoteric cobalt alloys. A motorized mechanism pushed disk drives past the magnets; a back up twist-knob allows operators to manually pull drives through the magnetic field.
How did they determine it really worked? By using the same techniques a serious disk recovery effort might use
The team verified that it was impossible to recover information from disk drives erased with the permanent magnets. They used a magnetic force microscope to map even the smallest magnetic domains on the surface of an erased disk drive to ensure that the patterns found there were completely random.
Disposing of disk drives that contained important information? Be even more paranoid than you are now.
The solution is much easier. On-Disk-Encryption and throwing away the key. There are some ideas to integrate this into ZFS (look here: http://www.c0t0d0s0.org/archives/1447-Even-more-about-ZFS.html). By this mechanism you can even delete disks that are not in reach.
Given that the folks building the solution are US defense contractors it is probably not safe to assume they considered such a low-cost option. Yet against a determined reader with essentially unlimited time, probably most any encryption scheme could be broken. And the other big problem: how do you lose the key quickly?
I assume, that they have access to more sophisticated encryption mechanisms than the public. And the encryption has not to withstand forever. Only for maybe 10 years or so.
Loosing the key is easy. CD in Microwave or magnetic deletion by the means described in your original posting. But with the advantage that all data is erased at once.
OK, so explosives won’t do the job but the super powerful magnet that can degauss the platters through the faraday cage surrounding the disk is overkill.
Instead they should use light explosives to quickly remove the disk platters shielding and then they can use a much weaker magnet to wipe the platters.