Star Trek: The Next Generation – Descent, Part II [7.1]

Data, under Lore’s thrall, conducts experiments on Geordi as part of Lore’s vision to destroy all organic life forms.  Realizing that in addition to feeding him emotions, Lore has also has dismantled Data’s ethical programming, Picard and the others attempt to find a way to restore it. 

Star Trek: The Next Generation – Descent [6.26]

During a battle with the Borg, Data unexpectedly finds himself experiencing a flash of anger.  Confused and concerned by his newly discovered capacity for emotions, Data finds himself lured by a Borg prisoner to set him free and escape with him to join his mysterious leader. 

Star Trek: The Next Generation – Brothers [4.3]

Data suddenly comes under control of a homing signal that brings him to the secret hideaway of his creator, Dr. Noonien Soong, which endangers an emergency medical mission that the Enterprise was undertaking.  The signal also brings Lore

Star Trek: The Next Generation – Datalore [1.12]

Returning to the destroyed colony where he was originally found, Data and the Enterprise discover and reactivate an identical android known as Lore.