What makes your account, on some website like "myspace" at all sacred and secured by laws? What defines an "account"? Does the person in charge of the account

What makes your account, on some website like "myspace" at all sacred and secured by laws? What defines an "account"? Does the person in charge of the account, in this case Myspace, have any obligation to ensure the security of your account? For example, what if Myspace only allowed a 1 digit password on your account. Is it still illegal to "hack" your account, or is it Myspace's fault?