Mon, 26 Oct 2009 Macworld Help: Securely wipe your hard drive

I’ve seen an ad for software that completely wipes hard disks by writing 0s and 1s on the drive in several passes. Is it genuine?
Jim Bradley

It certainly is, and you’ll doubtless be happy to know that the software is free and probably already on your Mac if you’re running Tiger or Leopard.

To begin the process of wiping your drive, launch Disk Utility (/Applications/Utilities) and select the drive you want to erase in the pane on the left side of the Disk Utility window. Click the Erase tab and then click the Security Options button below.

In the sheet that appears, you’ll see four options – Don’t Erase Data, Zero Out Data, 7-Pass Erase, and 35-Pass Erase.

The Don’t Erase Data option – as its name implies – doesn’t erase any data. Rather, it wipes out the directory that tells your Mac where your data is. Any number of third-party utilities could scour your drive and recover your data after you’ve employed this option. So that’s not secure at all.

Zero Out Data writes zeros over your drive one time, but can leave ‘ghost’ images of your data in some places. It’s possible for data to be recovered, but not very easily.

7-Pass Erase writes over your data seven times and actually meets the standards set by the US Government’s Department of Defense, but if even that doesn’t sound good enough, go for the 35-Pass Erase option, which, as the name states, writes junk over your drive 35 times. If you want your data super-mega-ultra-really gone, this is the one to use.

Note that the 7-Pass Erase option takes seven times longer to overwrite your data than does the Zero Out Data option. Likewise, the 35-Pass Erase option takes 35 times as long.

If even these options leave you feeling slightly paranoid that you still haven’t done enough, then we have one final solution to propose to you – the Multi-Pass Sledgehammer option. Should you need absolute certainty that your data will be completely and utterly unrecoverable and are willing to sacrifice a hard drive to make that happen, we suggest extracting the drive from your Mac, taking it out into the garden, donning a pair of safety goggles, and beating the living daylights out of it with a sledgehammer!