Re: "...unencrypted..."
Sarbanes-oxley should provide the needed law broken if storing CC information, which target did. i do not think there is any law on the books that can be used to charge for criminal neglect of personal data in this instance. the criminals are the people who did the hacking.
the part that should be prosecuted to the fullest extent as complicit in the crime itself is the people at target who attempted to cover up the crime.