security - How can I physically destroy data from a failed HDD?

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?

Answer

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.