Rain of Terror

The Rain of Terror was created by the Ulla people on Xirrinda. Their technology had gotten out of control and they had practically destroyed their planet. The creatures were created to rid them of their sins.

The creatures were an accident. They travelled the galaxy, devouring whole planets and then multiplying thousands of times each second. Because of their size they caused massive gravitational interference. Ships couldn't lift from the ground and all machinery was turned off.

The Eleventh Doctor called them a machine and not a species because that was what they really were. They were defeated by the machine the Ulla people had devised to destroy them in the first place. (NSA:  Rain Of Terror)