Variant 7

Variant 7 was a type of drug created by the Daleks for getting high of their arses. The NFS plague that had engulfed the inhabitants of the galaxy was caused by this drug.

It was part of an elaborate plan by the Dalek Empire to boost their numbers after the Great Catastrophe. Variant 7 was provided to the individuals suffering from the plague which contained extra DNA embedded within it that remained dormant in the body. Once it was exposed to a certain form of radiation, this additional DNA converts the host into a new Dalek, allowing for the Empire to create a massive army. (BFDE: The Future)