Q The hard disk in my MacBook died suddenly, but thanks to a robust backup routine I lost little data. The disk will not show up under Disk Utility or System Profiler, or even Drive Genius or Data Rescue. It contained some sensitive personal information, so how can I make its files unreadable before I throw it away?
A Ordinarily, the best tool for obliterating the files stored on hard disks is Disk Utility.
Select the drive, click on the Erase tab, then the Security Options… button. You can then choose how many times your data will be overwritten by zeroes, opting for the most secure and taking the longest time if the files contained sensitive information. This is also detailed in this article.
As your old drive is too badly damaged for any utility to access it, it might be tempting to just throw it away. However the determined might still be able to read some of its contents, for example in a forensic rig.
If you are unable to zero out your files thoroughly, you should physically destroy the drive using a hefty sledge-hammer. Break through its casing and disrupt the platters and head inside. The process may also be effective at relieving the stress that its failure caused.
Updated from the original, which was first published in MacUser volume 27 issue 21, 2011.