Yeah, I'm aware of that. I meant something along the acid or small destructive (phyiscally) device on the hard drive. Self destruct button kind of stuff.
As far as this wiping thing goes. I got Norton Works a long time ago because I was having trouble. Installed the whole thing and used it for a while but have since uninstalled everything except the anti virus program. Norton's wiping utility offered "standard" or "government" as options. The gov't wipe if I recall inserted 0s and then 1s into all the blank space of your computer three seperate times and then did a random insert the final time before wiping the hard drive clean (if I'm not mistaken- I never used it). They can still get data after all that? How do they do it? If it's too long an explanation don't bother- but I am interested.
How I have no idea. But they claim they can, at least part of the time. Something to do with residual atoms from the original "imprinting" on the disk or something like that, kind of like how even if you take a cassette and tape over it, you can still just barely hear the original recording underneath, especially after going through some heavy-duty digital audio processing. (They're trying to resurrect the infamous 18-Minute Gap from the Nixon Tapes this way, without success thus far.)
If a particular bit of the disk has been magnitized in one direction for an extended period of time, it might retain a degree of "preference" for that state, even after being flipped a few times.