The Nanoforms were tiny robots that deconstructed objects on a molecular level and then reconstructed them into a new form. They needed to be kept at sub-zero temperatures to remain inactive. (TV: Prisoner of the Judoon)
The Nanoforms were created by Genetec Systems, but they could only make extremely minor modifications. Genetec falsified their results and claimed to be able to do more advanced tricks. When Sarah Jane Smith investigated them, she was thrown out of the building.
When Androvax later took over her body, she used the knowledge contained in Mr Smith to correct the problems, allowing the Nanoforms to work. She programmed them to reproduce, create a spacecraft to escape Earth and to then dissolve the planet. When Androvax was captured, Luke Smith was able to reprogram the Nanoforms to stop. (TV: Prisoner of the Judoon)