Answer:
Depends how bad you want to hide something. If the drive has previously been encrypted and the password hashed (like AES-256 with SHA-512 hashing), then deleting the content is enough since it will be slightly overridden and thus unusable. If it is not encrypted already, delete it, and override all your disk space with something. If you want it to die as a secrete 100%, burn it and pulverize it. Otherwise, if you want a quick method, use some real delete software.
