Movellan virus

The Movellan virus was developed by the Movellans to attack Dalek casings and tissue.

History
Its effects were immediate and devastating. Symptoms included loss of motor control and expulsion of a whitish, foamy substance from vents and seals in the Dalek's casing. The infrastructure of the Dalek Empire was so damaged by the virus, the empire broke into factions and fled to distant parts of the universe to avoid infection and find a cure. (TV: Resurrection of the Daleks)

According one account, the First Movellan was inspired to the create the virus when Davros attempted to spread a computer virus throughout the Movellan network. (AUDIO: The Triumph of Davros)

Davros was rescued by the Black Dalek Leader to develop a cure. Davros instead tried to use the virus to destroy the Daleks loyal to the Supreme Dalek and subsequently develop Daleks completely loyal to him. However, Davros' Kaled tissue proved vulnerable to the virus and he began to display symptoms before escaping captivity. (TV: Resurrection of the Daleks) According to The Lives and Deaths of Davros, his analysis had been sent to Dalek Supreme Command, allowing for the Daleks to synthesize a cure for the virus. (PROSE: The Secret Lives of Monsters)

The Thals later developed a concentrated form of the virus, a thousand times deadlier. It would kill immediately, spreading throughout the entire Dalek race in seconds if it was released on Skaro. (AUDIO: The Davros Mission)

During the Great War, the Daleks were driven from Mars by a virus that was hypothesised to be derived from the Movellan virus. (PROSE: The Whoniverse)

During the Last Great Time War, the TIme Lords had a sample of the virus cultured in laboratory condition but early tests suggested that the Daleks had succeeded in gaining immunity. (PROSE: Dalek Combat Training Manual)