Yes, we have discovered cold fusion, because there have been great scientific discoveries. Just that we have discovered it, though, does not necessarily mean that it is the most efficient or promising way of producing nuclear energy. But it is true that we have done a great deal of work in the field and we have made progress.
We have not discovered cold fusion. When we do, you will actually know about it, and it will be something that is not just speculated on. There is no benefit for scientists hold back this information from people and that is why I can say that we have not discovered it.
I do not believe we have discovered cold fusion yet. It is still considered a hypothetical situation and it is still being studied. Ideally cold fusion would make nuclear energy far more safe, so hopefully we will find the solution in the future. It is helpful because it proposes the idea the reactions could occur at a room temperature rather than the atronomically high temperatures required at this time.
Cold fusion, while plausible, has not yet been discovered. It is still theoretical and being worked out by scientists. Theoretical doesn't mean there's a bunch of opinions, it means the evidence is there and they are working on how to make it happen. We will all know once it does.
If anyone on this planet had discovered cold fusion, there would be no way of hiding the news. The sheer size and complexity of such a project could be hidden for a while potentially, but the actual success of such an endeavor would mean too much to potential energy production. No company or nation would benefit from having it but keeping a secret.