Try "shred".  It's part of the GNU fileutils, and should be present on
your system.  You'll probably want to shred the entire device, e.g. 

   shred /dev/hdc

You could also use alternating dd passes, provided you had an all-ones
source to go with /dev/zero.  /dev/urandom might do in a pinch.  I
wouldn't depend on shredding at the file level; the man page indicates
that file system behaviors may not produce the desired result.

If you're running OpenBSD, FreeBSD or NetBSD you can also use "rm -P",
apparently.  

On Mon, 20 Jan 2003, 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
> 
> -- 
> *-----------------------------------*
> | Dustin Decker                     |
> | dustind@moon-lite.com       *-----------------------------------------*
> | http://www.dustindecker.com | Even in evil, we discern rays of light  |
> | Moon-Lite Computing         | and hope, and gradually come to see,    |
> | 913.579.7117                | in suffering and temptation, proofs and |
> *-----------------------------| instruments of the sublimest purposes   |
>                               | of wisdom and love.                     |
>                               |		-- William Ellery Channing      |
>                               *-----------------------------------------*
> 
> 
> 
>