Possible Clues:

• It's already out of the bag
• It's thinly disguised
• Respect one formulating a 'known unknown'
• Supposedly confidential but actually widely known matter
• Widely known fact that isn't supposed to be widely known
• Supposedly unknown but actually widely known fact
• Unspoken shared knowledge
• It's known by many but is not supposed to be
• Highly confidential matter that like a billion people know about
• It's hush-hush in theory, but not in practice