I guess your missing my point:
If you just wipe the dist by flipping the bits, the data can be re-read be
reading the residuals on the sides of the tracks. Now you just need some
cool info-processing software (like FFT, and who know what else) to be rid of 
the noise, and get the original back.

To truly wipe the disk, wouldn't you have to flip the bits 3 to 10 times --
depending on the security desired?...

-- 
Have you ever killed anybody? Well I hurt somebodies feelings once...--R. Deniro--