They're not allowed to prove it. It's a scandal that they are even asking the question - someone was fired for it.
I'm not sure what that means. Facebook can surely say "hey the PR firm we hired told the truth and here it is", but as far as I know they've chosen not to.
I'm not sure what that means. Facebook can surely say "hey the PR firm we hired told the truth and here it is", but as far as I know they've chosen not to.