.... for the sake of fun.....
How likely do you think it is that aliens have contacted the major world governments with specific instructions not to make their presence known to the public? Do you think our governments would be in a position to refuse?
Do you think the aliens might make other demands? What do you think would motivate this contact? Desire for access to our natural resources? Altruistic desire to prevent us from nuking each other? Boredom?