Simple Hard Drive Reformat Code

Hello, I am currently learning C and Java and I am bored! I would like to make some kind of virus or code that will mess a computer up! I am studying computer security so this stuff interests me. I would like some help with simple code in order to do this. I was thinking about a program that will identify the largest hard drive in the system and reformat it. Any help would be appreciated. This is just for fun and to learn the language more in depth. Thanks