This explanation contains SPOILERS for the series Generator Rex. This is just a handy reference guide for anyone who wants to know what the big deal about nanites in Six's world. Any suggestions for how to better improve it are welcomed.

Spoilers are behind the cut.

What is Commonly Known

Five years before the current time, a group of scientists came together to work on nanomachines called "nanites" with the intent to cure disease in what is referred to as "The Nanite Project". A very noble goal by anyone's standards.

Unfortunately, there was an accident. The research lab in Abysus was mostly destroyed due to a massive explosion. This explosion, commonly known as "The Nanite Event", became the most significant disaster in human history. The nanites--their programming still unfinished--were released and spread across the world, infecting every living thing on Earth: every human, every animal, and every plant. Due to their unfinished programming, the nanites started mutating whatever they infected. A tiny minority of humans who were changed managed to keep their minds and some measure of control over themselves, but for the most part the changed became rampaging mutating monsters that would later become known as "EVOs" (short for "Exponentially Variegated Organisms").

Most of the time, the nanites in a person's body are dormant. That person can go about his or her life for years without any issues from them. However, should those nanites ever activate, the mutation will occur. What exactly triggers nanite activation is unknown. One person might transform in the middle of a high-stress situation. Another might be in the middle of book while relaxing.

Kiev in the Ukraine was the hardest hit due to the Earth's magnetic field concentrating so many nanites there. Almost every living thing went EVO. In response to widespread panic, all unchanged citizens were evacuated and a spherical force field was put in place around the city to hold the EVOs in, all access to it banned. This became later known as "The Bug Jar".

Several containment groups were founded around the world, the largest of which being Providence. Providence started out containing or killing EVOs. However, it gained more prominence due to researching a permanent cure for EVOs. The "kill" option became the last resort should cure (using an amnesiac boy who could deactivate nanites named "Rex") or contain fail.

( The Truth Behind the Truth (SPOILERS) )