[yevgenie]

Not a myth!
Yes, it is true that you CAN repeatedly rewrite over the disk surface. The problem is that many HDD's are not quite so precise in the movements of the head and the platter. Sometimes this results in a shift in the position of the head over the platter and there may be a residual charge left on the surface even after someone has "correctly" attempted to overwrite the data.
-Yev (computer security specialist)

[Glenn]

The problem is that many HDD's are not quite so precise

With the density and sophistication of controllers, the odds of what you describe are pretty long in this day and age. Don't you think?

[proxy_user]

Yes, Yev, but if you follow the DOD standard (7 x overwrite) usually some bits are unrecoverable. This leaves you with te t wi h let rs miss ng, so what was there has to be reconstructed. It's absolutely hopeless for binary files, such as most databases, spreadsheet, and word processing programs produce.