Personal theory on why Governments have not publicly announced the existence of extraterritorial life

It would cause wide spread panic. People would demand answers on why the public was kept in the dark about it, people thinking it is some alien invasion, religious folk would see this as sign of the apocalypse or something along those lines. In all honesty it seems like the most likely theory on why we have never been told anything, maybe the Government figures have some sort of pact with whatever aliens are out there that are stopping them from telling us. Thoughts?