I came accross this today while browsing. Seems that we might have received a reply to a message sent out by SETI in 1974. Makes for an interesting read if nothing else.
Arecibo Message
Yes, interesting. I think the main reason I would tend to question it's authenticity is that whoever left this "reply" clearly understood every aspect of the original SETI message that was sent, which seems fairly unlikely to me. I doubt there would be many humans who would even understand part of it's meaning if it wasn't explained to them by the people who came up with it...
I heard that the Chilbolton message was fake..The Arecibo message would arrive in the year 26,000.. and take the same amount of time to reply, if they are as advanced as us..
Arecibo Message