Just as it’s difficult to completely erase data from a hard drive, it’s even more difficult for some of the newest solid state storage devices.  There are some military grade programs that will erase the contents of a hard drive (changing everything to binary zeroes).  These should be used for disposal or equipment resale purposes.

Solid State Drives – Difficult to erase deleted data

QUOTE:  Even most novices know that erasing a file doesn’t necessarily remove it for good. Fully erasing data can be much trickier than it seems. And now it seems that the newest forms of storage are the hardest to erase. At this week’s Usenix FAST 11 conference on File and Storage Technologies in San Jose, California researchers published a paper examining the effectiveness of different secure erasure methodologies on Solid State Disks (SSDs). It turns out to be tricky.

Kim Komando offers free utilities to safely delete all hard drive information