The rest of the people work for the government, not the corporation? All they need is someone inside the company whose job it is to keep other people inside the company from finding out. It's the same model as police use for informants and intelligence services use for espionage.

It's also kind of pointless to talk about how to falsify a class of thing we have affirmative evidence is happening. When we found out about PRISM, the heads of the companies said they didn't know anything about it. So either they were lying or their subordinates successfully kept it a secret from them.

Moreover, the interesting question isn't whether it's happening right now. It's that given we know it can happen, how do we prevent it from happening? For example, by using software with published source code that runs on your own device instead of someone else's.