From the Daily Mail:  Computer hard drive sold on eBay ‘had details of top secret U.S. missile defence system’

I think that headline pretty much speaks for itself.  I’ll just throw in a plug for the Kanguru Hard Drive Duplicator, which has built-in hard drive wipe functionality.  The HDD Duplicator uses a data wipe algorithm complying with US DOD 5220-22.M Standard.  Simply deleting or re-formating a drive is not always sufficient to make data unrecoverable.

Data Security, Duplication