Cybonic Plague is a virus that is transmitted through infected energon. The virus, once it has entered its victim, will slowly infect the victim's energon supply and causes a fatal shutdown.
Cybonic Plague was engineered in the Decepticon's biological warfare program during the Great War. It's creation was ordered by Megatron himself. The virus killed millions of Autobots during the Great War. Energon infected with Cybonic Plague takes on a purple coloration. The virus itself is contracted by coming into contact with infected energon.
After the distress beacon of a crashed Autobot ship was detected, Optimus Prime and Ratchet went to investigate it. While in the ship, Optimus became infected by the virus. The Autobots then elected to enter the Nemesis to look for a cure, believing that if Megatron created the virus, he would want to have a cure for himself.
Though the ship's data banks did not have the cure, they found that Megatron was still online, albeit in stasis. Bumblebee then used a Cortical Psychic Patch to enter Megatron's mind to find the cure. While inside, Bumblebee met Megatron's mental impression of himself and convinced him to to give up the cure for Optimus so that Megatron could terminate Optimus himself when he woke up.
- The plague is probably a reference to the Bubonic Plague. The Cybonic Plague also creates a purple color change on skin and killed off millions of Cybertronians. The Bubonic Plague creates a pink hue color change on skin and killed off millions of Europeans in the mid 1300s.
- Ratchet was testing Optimus's eye to make sure the Cybonic Plague was clearly cleaned off of him at the beginning of "Out of His Head".