Secure erasing deleted files
Deleted files can be easily tacked by data-recovery software, so if you have sensitive files on the hard drive, it is better to erase them after deleted.
Erase is to overwrite sectors that deleted files once in with meaningless data, in ByebyeData eraser, you can use one of fourteen overwrite methods to fill the deleted space.
Click Erase free space in the main window, then select the drives deleted files were stored on > select an erasing standard > Erase Now > Click Yes to the confirm dialog.
it is always recommend to backup before Erase any hard drives, but you don't need to do this when you're erasing free space, on account of erasing free space will not touch data currently in each folder or drive, this operation only deals with deleted space, unused space and free space you never used.
Apply to Windows 10, 8, 7, Vista and XP