Creative Speculation

Great big universe, ergo, some possibility that intelligent life has developed elsewhere. Probably not very nearby, so the civilization whose signals we detect could be gone, or else radically transformed, by the time we detect and decode them -- never mind find a way to carry on a conversation. Of course that's why so many science fiction novels stipulate a means of faster-than-light travel or at least communication. At any rate, it's an interesting question. Of course, I would think so, having been raised on Star Trek.

For what it's worth, (1) I think it would be hard to keep extraterrestrial communications secret (although I can imagine a scenario in which it is feasible), and (2) given the premise of the question, I think we should construe that we've been saying "Hi" for a while now.