It's foolish to assume that there is no other intelligent life in the universe. There are probably thousands or millions of intelligent species. But honestly, why would they care about us? Oh, look, we made a big explosion. Chances are, if they had the technology to come to our planet, they could make a significantly larger explosion. We have the internet? They probably have a telepathic network which links into every "computer" in their empire.
For a race to have come this far, it would have to be extraordinarily advanced, and it would probably have better things to do than infiltrate a group of misfits like humanity. Not to mention the fact that they would look nothing like us.
Oh, and if the US government tried to capture them, they would probably destroy the US government.
(Former) Lead Moderator and (Eternal) VGC Detective 
