http://www.heise-online.co.uk/security/Sec...t--/news/112432Secure deletion: a single overwrite will do it
The myth that to delete data really securely from a hard disk you have to overwrite it many times, using different patterns, has persisted for decades, despite the fact that even firms specialising in data recovery, openly admit that if a hard disk is overwritten with zeros just once, all of its data is irretrievably lost.
Can Intelligence Agencies Read Overwritten Data?
http://www.nber.org/sys-admin/overwritten-data-guttman.html
The Great Zero Challenge: