The leaked information was all a ruse. The scheming Emperor Palpatine engineered the Rebellion's discovery of the Death Star in the hopes of trapping the growing Rebel fleet. The second Death Star would not be as vulnerable as the Rebels believed.
To ensure that the Death Star would destroy the lured Alliance fleet, Palpatine entrusted the supervision of its final phase of construction to his Sith apprentice, Lord Darth Vader. Vader motivated the Death Star's commander, Moff Jerjerrod, to see that the battle station was operational when the Emperor arrived for his inspection tour.
The second Death Star was not a complete sphere. Though much of the battle station's recognizable shape was visible, there were huge sections of exposed superstructure and visible skeleton. To protect the half-completed and immobile station during its construction, the Empire projected an immense deflector shield from the nearby forest moon of Endor. The shield was strong enough to protect any breach from both capital and starfighter-class ships.
The Alliance sent a commando team to land on the moon and deactivate the shield generator while the Rebel fleet emerged from hyperspace to destroy the station. Unlike the previous Death Star, whose reactor core was accessible only from a two meter wide exhaust port, the second Death Star's heart had to be destroyed by actually flying into the superstructure and detonating the collosal power plant.
The commando team was waylaid by Imperials and the Rebel fleet arrived to find the deflector shield intact. Worse yet, the superlaser was operational, and began destroying Rebel Mon Calamari cruisers with each blast. General Lando Calrissian came up with a daring and foolhardy tactic to engage the Imperial fleet at point-blank range, thus limiting the Death Stars available targets.
Aided by the native Ewoks of Endor, the Rebels were able to infiltrate and destroy the shield generator complex. With the shield down, General Calrissian led the Alliance starfighters into the inner recesses of the Death Star. There, he and Wedge Antilles loosed a volley of ordnance that began an immense fireball that tore apart the station.
Emperor Palpatine's body was consumed in the explosion. The Imperial fleet never recovered from the fiasco. What was to be the Rebel Alliance's demise instead turned into the death of the Empire. As firey fragments of the battle station burned away in Endor's atmosphere, the celebratory cheers of freedom rang throughout the forests, and indeed, the entire galaxy.