Do you have a file on your computer that you want to obliterate? Well, it’s going to take a lot more than dragging and dropping it into the little trash can at the corner of your desktop. Your computer’s trash bin only removes a file from your desktop. And even if you empty the trash bin, it only deletes the virtual pathway to it. The file is still saved in your hard drive, but now it’s just more difficult to access. There are a few easy and effective ways of getting rid of that file once and for all, and they all involve overwriting the file with other data.
Source (Sylvan Lane, “How to Delete Something Permanently From Your Computer”, Mashable, 14.07.2014)