Had information been made public that the AI Council made Contact with aliens in the Twenty First Century the stress to our societies may have been catastrophic. But the AIs had a plan, you see. They did not wish Contact to come from on high, with alien starships coming from the heavens to a primitive Earth that had barely achieved space flight. They wanted our starships to meet in space after we had colonized a few dozen star systems and become an interstellar power in our own right. So the AIs Contacted the Peloran watching Earth and asked them to keep their distance for a time. Admiral Aneerin of the Peloran Confederation agreed with them whole-heartedly, and offered them any help he could provide in accelerating that happy outcome. The AIs were quick to accept his offer, which I suppose explains many of the scientific advancements of that century. It would seem that some of the conspiracy theorists may have been right after all.