How Secure is a Secure Erase in Disk Utility?

I've been reading about the Secure Erase options in Disk Utility. The 7-pass erase and the 35-pass erase in particular.

This article gives an overview of the differences between the 7-erase pass and the 35-erase pass. I've decided to ignore the write zeros to disk option since it should be clear to most people that is pretty ineffective in real data scrubbing.

The 7-pass erase is based on the DoD 5220.22-M specification which demands 3 passes conforms to scrubbing data at a military standard. The Google Cache for the document describing this specification is available if you search for 5200.28-STD.

The 35-pass erase is a totally different beast. The implementation is based on research at the University of Auckland in New Zealand. The method uses information about how data is originally written to a magnetic disk in order to provide the best possible scrubbing of data. The author of this report notes that nothing short of using an extremely powerful magnet can guarantee the probable removal of data - and he cites a powerful navy magnet that actually warped the disk platters as a suitable magnet.

You might wonder why I am blogging about this? Well I found it to be interesting and I always wanted to know more about the implementation that Apple's Disk Utility uses and maybe now you can know more too.