The assumption should be this:
Anything that is said to anyone else may well become public knowledge.
So the key to confidentiality is to keep information on a need to know basis, and be constantly challenging who actually needs to know.
The greater the members of an organisation, the exponentially greater the communication pathways.
And so the best way to keep things secret is to to keep it to an inner circle, and when in doubt, reveal less than required.
Of course, we are getting ahead of ourselves, we should first ask if and why secrecy is required in the first place.