Utility Fog self-replicating in the Yeyeos mountains on Escelon 3
Part of the Puppis Democracy. A number of dissidents from Novoterra were exiled to Escelon 3, where in 9745 they set to quietly convert parts of the mountain range into utility foglets in order to take over the planet.
When discovered a major nanotech war broke out on the surface, devastating 33% of the biosphere before the defenders could wipe out the fog. As the dissidents were themselves part of the ufog, they were also wiped out in this war.