Star Trek: The Next Generation - Descent(1995)

The Enterprise is diverted to Ohniaka Three, when the colony signals that it is under attack. Arriving at the outpost, the Starfleet Officers discover that a previously resisted enemy has returned. The Borg are now more hideously powerful than ever before. Having discarded their relentless behaviour, they now display individuality, are possessed by ruthless aggression and will attack on sight. This terrifying turn for the worse is blamed on Captain Jean-Luc Picard because of his earlier leniency on an adolescent Borg. During the fighting, Data experiences his first emotion and discovers that his evil brother, Lore, has joined the Borg.