I wonder what the theoretical limit is for the number of people that can retain a secret actually is, with modern technology and all. e.g. governments definite

I wonder what the theoretical limit is for the number of people that can retain a secret actually is, with modern technology and all. e.g. governments definitely keep secrets, so how many people can be in on a given conspiracy-like government secret without major leaks that cannot be squashed through media, suppression, etc.? I feel like precursors to the Manhattan project (since the project itself was clearly widely known) would hold the answer, but wouldn't account for modern technology / communication methods. An interesting / fun thought :)