Any information can be protected using a Non-Disclosure Agreement (NDA) so long as both parties agree for such information to be protected. The confidentiality obligation of the NDA may be express or implied depending on what the parties to the NDA agree.
Some parties will agree that only information expressly stated to be confidential is protected by the NDA whilst in some NDAs, the parties agree that any information relating to the contemplated transaction will be assumed to be confidential.