The days when you could actually address (work on) a specific part or area of a storage device are long gone, so overwriting the old data to securely delete it

The days when you could actually address (work on) a specific part or area of a storage device are long gone, so overwriting the old data to securely delete it is no longer possible/guaranteed. A fair overview of Data Remanence is on wikipedia. You want to pay attention to the issues mentioned with flash based (SSD) storage as well as the links to the various research papers. http://en.wikipedia.org/wiki/Data_remanence http://en.wikipedia.org/wiki/Data_remanence