I wish I could find the article, but I can't right now.  In short, the only 
way to securely erase data from any magnetic media is to burn it.

In the article I read, which contained technical details on different 
magnetic media and what it would take to erase all traces of data, this is 
what they suggested.  The article talked about some of the most detailed 
erase methods and they still didn't remove all traces of the data.  If I 
remember correctly, the people that did the research applied enough 
magnetic force to a hard drive to bend the platters but were still able to 
read data from the platters.

On Monday 20 January 2003 15:13, Dustin Decker wrote:
> Howdy all,
> I have an intersting project on my plate at the day job.  Once in a blue
> moon (prolly more like each full moon) we overnight a 30GB Iomega USB
> drive to a client, they put a backup of their database on it (between 4
> and 10 GB) and ship it back to us.
>
> Eventually, the drive will be sent to another client.  We're dealing with
> personally identifiable information in the health care mode here, so in
> the interest of avoiding a HIPAA snaufu I'm quite serious about ensuring
> that there aren't any traces of the previous clients' db on the drive
> when it ships.  I've been making use of BCWipe on the Windows platform to
> accomplish this to the DoD 5200.28 standard, but I'm interested in
> throwing this on a Linux box to get it done as this is an extremely time
> consuming process.  (Would prefer to start it on Linux and walk away.)
>
> Any suggestions on utilities in the Linux world that can do this?
> Dustin