Hey,

if your business is security related you have to delete your files in a secure manner. For windows there are some tools like eraser [1] available. For debian based linux systems you can apt-get the secure-delete package.

Code:
apt-get install secure-delete
then you can use "srm" for deleting the secure way or you can use "sfill" for deleting the unused disk space in a secure way. There are some more tools in this package ...

hf
m-1-k-3

[1]: http://sourceforge.net/projects/eraser/