How ro protect against CryptoLocker (ransom) type Trojans

Norton Security | Norton Internet Security
1

For active protection I use NAV 2014 (21.6.0.32) fully patched and MB's Anti-Exploit 1.05.3.1012 (experimental).

I have an external USB3 WD My Book Duo 4TB (setup for Raid1), which I use for backup archiving only.  As CryptoLocker and similar (ransom) Trojans encrypt and lock external drives, as well as internal ones, is there a way - other than to unplug or remove the USB drive when not used - to protect the My Book Duo while connected?

For example, would the My Book Duo hardware password (256-Bit AES encryption) help?  Or, would the ransom Trojan encrypt the (encrypted/password-protected) external USB drive regardless?  Any suggesions on how to keep the My Book Duo online - safely - at all times?

Thanks.