Self-replicating nanotech devices that spread uncontrollably, building copies of themselves using all available material. Consists of a disassembler swarm (Black Goo) combined with assembler units programmed to create more Grey Goo. In practice, truly 'universal' Grey Goo is unknown, though there are some very versatile goo swarms, usually of transapient design, that can live on a wide range of materials in very broad ranges of environmental conditions. Though the Grey Goo units of popular fiction are often the size of dust particles, actual Grey Goo is most effective when it includes a variety of sizes, from microscopic on up to 'digester' units weighing hundreds of kilograms that break up materials for use by smaller units.
Truly accidental cases of Grey Goo are debatable; it may well be that most or even all Grey Goo incidents are intentional, and that in apparent disasters there is some responsible hostile party who has simply not been identified. The worst-case scenario where a sufficiently sophisticated Grey Goo weapon is deployed is the complete conversion of a world's or hab'secosystem and/or mechosystem into suites of Grey Goo units. This scenario has rarely happened in reality, one of the few cases being the destruction of Makintairas during the Second Consolidation War.
In most cases Grey Goo forms part of a larger Khaki Goo attack, incorporating many forms of self-replicating weapon. In most cases, modern Grey and Khaki goo attacks can be defeated rapidly by suitable Blue Goo defences if they are caught in the early stages.
Makintairas - Text by M. Alan Kazlev 10 Tauri - inner sphere system, destroyed by grey goo swarms during the Second Empires War - Metasoft was wrongly accused of the atrocity by a number of anthropist extremists and anti-vec propagandists of the time.
Paste - Text by Steve Bowers Swarm devices manufactured by a forge system, (such as a bioforge or nanoforge) so that the individual units do not carry the code for their own replication (human red blood cells are an example of this in biology).