First contact with an alien civilization will be a momentous event in the history of Earth. Unless the other civilization is kind of a dick. Tim Urban didn't quite cover this scenario in his post about the Fermi Paradox.
kottke.org posts about Enrico Fermi
Edward Snowden's Fermi Paradox solution Sep 21 2015
Edward Snowden has come up with a solution to the Fermi Paradox that I hadn't heard of before. Maybe we haven't discovered intelligent life elsewhere in the Universe, says Snowden, because their communications encryption is indistinguishable from cosmic background radiation.
"If you look at encrypted communication, if they are properly encrypted, there is no real way to tell that they are encrypted," Snowden said. "You can't distinguish a properly encrypted communication from random behaviour."
Therefore, Snowden continued, as human and alien societies get more sophisticated and move from "open communications" to encrypted communication, the signals being broadcast will quickly stop looking like recognisable signals.
"So if you have an an alien civilization trying to listen for other civilizations," he said, "or our civilization trying to listen for aliens, there's only one small period in the development of their society when all their communication will be sent via the most primitive and most unprotected means."
After that, Snowden said, alien messages would be so encrypted that it would render them unrecognisable, "indistinguishable to us from cosmic microwave background radiation". In that case, humanity would not even realise it had received such communications.
Snowden shared his hypothesis with Neil deGrasse Tyson on Tyson's podcast, StarTalk.
What else is out there? Jun 26 2014
Great post on the Fermi Paradox, aka if there are so many potential intelligent civilizations out there in the universe (possibly 10 quadrillion of them), why haven't we heard from anyone?
Possibility 5) There's only one instance of higher-intelligent life -- a "superpredator" civilization (like humans are here on Earth) -- who is far more advanced than everyone else and keeps it that way by exterminating any intelligent civilization once they get past a certain level. This would suck. The way it might work is that it's an inefficient use of resources to exterminate all emerging intelligences, maybe because most die out on their own. But past a certain point, the super beings make their move -- because to them, an emerging intelligent species becomes like a virus as it starts to grow and spread. This theory suggests that whoever was the first in the galaxy to reach intelligence won, and now no one else has a chance. This would explain the lack of activity out there because it would keep the number of super-intelligent civilizations to just one.
Update: If you prefer to watch engaging videos instead of reading text, here's six minutes on the Fermi Paradox: