C Lion said:
Delete C drive, solve problem.
The problem with that is that, even after a normal deletion, it's a straightforward and somewhat simple process of 'undeleting' the files.
Files on a hard disk leave a signature there, even after they're erased. You'd need either a special type of program to overwrite the files a zillion times after they're deleted, a powerful magnet, or destruction of the drive to make sure they're gone permanently. All three wouldn't hurt if you wanted to make absolutely certain.