My friend gave me a one of his old harddrives so I could use it as a secondary hdd on my home desktop. However, to protect his privacy as well as clear all the space being used I want to delete everything that was on it. I tried manually deleting everything however there is still some stuff left on it (ie. operating system etc.) and I heard that it's still not very reliable or secure. Therefore I am wondering if anyone knows a way for me to completely delete everything on the harddrive including the operating system?