How can you wipe a Mac hard drive clean?
Mulder, would you mind explaining to us how you recovered data from a hard drive that had been wiped once?
You insert the installation disk from the most recent version of Mac OS X that you have, restart and hold down the 'C' key until you see the Apple logo.
Select your language, then go to the menu bar at the top and select Utilities > Disk Utility from the menu.
When that opens, select the icon for the hard disk of your Mac, then click on the Erase tab in the main section of the window there. Choose a Volume Format "Mac OS Extended (Journaled)", then click on Security Options and select the 7-pass option to zero out your data.
Then click the Erase button and confirm, and wait for it to be done; it will take hours, so you might as well watch TV, read a book, etc., while it's erasing the hard drive. You should check on the progress every few hours to see how much time is remaining.
Depending on the size of the drive and speed of the Mac a 7-pass erase may take days...
Unless the drive was used for very sensitive data like bank or credit card details stored in plain text a single pass is perfectly fine.
Duo to the data density on modern drives even a magnetic force microscope is no accurate way to determine the previously stored data.
"Duo to the data density on modern drives even a magnetic force
microscope is no accurate way to determine the previously stored data."
Not true. Writing zeroes to the drive with one pass is not secure and data can be easily recovered; I've done it myself many times, and there are a variety of software tools available to anyone for that purpose.
The 7-pass zero option is the DoD standard, and although it goes take considerably longer, no usable data can be recovered by any ordinary means; that's why the DoD uses it.
But if you throw enough money, time, and technology at it, you can recover data even from that or 35-pass zero options. Luckily, in order for that to occur, the interested parties would need to know in advance that there was something worth all that effort to recover.
Everything is impossible until it's possible.
— Jean Luc Picard
How is a software supposed to recover magnetic "1" if the hard drives head and controller reports only magnetic "0" to the computer?
It's a hardware/firmware limitation not a question of the right software solution.
The reason why a single overwrite is not government compliant is because data could still be present in bad blocks, software errors causing the overwrite process to skip [weak] blocks or simply data hiding in blocks outside the partition which is being zeroed.
The ATA Secure Erase command for example also does a single overwrite but on the firmware level and therefor over the entire drive including bad blocks - it is compliant to many government erasure standards.
You obviously didn't read what I wrote, and you clearly don't understand the process involved. You cannot erase a hard drive by any means known today with one pass; it's as simple as that.
Then what software or method did you use to recovery the overwritten data?