Whatever Rezbits were originally used for its quite clear the Luminoth wanted them in abundance. Special replicating devices are made only to create and copy Rezbits. Sadly Rezbits eventually corrupted these and only Rezbits that can be spawned from the machines have the Virus. It is unknown weather or not the ING are responsible for the virus that corrupted the Rezbits but that is one of the easiest theories to believe because the ING were known for corrupting machines of the Luminoth. Rezbits tend to attack individually and have been known to try to transmit the virus to living organisms but failed.