The Scourge crisis, alternatively called the droid plague or the "scourge of the droids," refers to a devastating infection that afflicted droids and cyborgs. This crisis engulfed the entire civilized galaxy during the Galactic Civil War, following the defeat of the Crimson Dawn syndicate. During the climactic battle of Crimson Dawn's war against the Sith, Lady Qi'ra opened the Fermata Cage in an attempt to imprison the Sith Lords Darth Sidious and Darth Vader, who ruled the Galactic Empire. By opening the Cage, a small disc fell out. Unknown to the two Sith, this was a piece of technology that the ancient Sith had locked away. After the Knights of Ren interfered with the Cage, freeing the two Sith but unleashing the Force Wave as a consequence, Qi'ra's forces were decimated by the Imperial fleet. One of her allies, the anti-Sith artificial intelligence called the Spark Eternal, escaped into the disc after the Dawn's destruction and merged with the technology the ancient Sith had tried to suppress, giving rise to the "Scourge."
The newly formed entity developed an insatiable hunger and propagated itself as a droid infection to access their memory banks. This Scourge infection caused widespread disruption within both the Empire and the Alliance to Restore the Republic. Fueled by its growing corruption of droids, the Scourge recognized that halting its spread would lead to its demise and initiated a campaign to dominate the galaxy, aiming to control the Force. The Scourge infected droids and cyborgs, seeking a way to conquer fully organic beings, with the intention of assimilating every being in the galaxy. This would eliminate any potential resistance. Consequently, the Scourge could fully immerse itself in the memories and information it had gathered during its expansion. Vader, as a cyborg, was the Scourge's primary target due to his vulnerability to corruption. The warrior-priest droid Ajax Sigma played a crucial role in stopping the Scourge.
After his failed attempt to punish his Sith Master Darth Sidious during the prevented Scourge of Coruscant, Vader willingly merged with the Scourge, hoping to surpass his master in power. It remained unclear whether the Scourge controlled Vader or if Vader had seized control of the Scourge for his own purposes. Ultimately, Vader quickly isolated his armor from the larger Scourge and attempted to create his own version of the infection under his command. During the Battle on Epikonia, the Scourge finally learned how to transfer itself into organic beings and seized control of Luke Skywalker's body. Through Skywalker, the Scourge declared its intention to become the new Force. However, at that precise moment, Sigma destroyed the Scourge's central body, liberating all organics, including cyborgs, and droids from its control.