Did Earth get a message from aliens?

In many ways, it's a scientific dream come true, a fantasy even to be indulged during daydreams. Usually it goes something like this. You're sitting at your desk where you monitor some telescope or communications equipment. Suddenly you see something unusual, interrupting endless hours of monotony. It's some kind of signal, something you've never seen before, something that can't have come from any Earth source and isn't produced by any natural p