Singularity Sky by Charles Stross
In the twenty-first century man created the Eschaton, a sentient artificial intelligence. It pushed Earth through the greatest technological evolution ever known, while warning that time travel is forbidden, and transgressors will be eliminated.
Distant descendants of this ultra high-tech Earth live in parochial simplicity on the far-flung worlds of the New Republic. Their way of life is threatened by the arrival of an alien information plague known as the Festival. As forbidden technologies are literally dropped from the sky, suppressed political factions descend into revolutionary turmoil.
A battle fleet is sent from Earth to destroy the Festival, but Spaceship engineer Martin Springfield and U.N. diplomat Rachel Mansour have been assigned rather different tasks. Their orders are to diffuse the crisis or to sabotage the New Republic's war-fleet, whatever the cost, before the Eschaton takes hostile action on a galactic scale.