The Grey Death is a powerful biological weapon/nano-virus that appears in the game Deus Ex and is a bio weapon used by the Majestic-12 Organization. Its main purpose is to destabalize peace and have MJ12 take over the world.
The Grey Death itself is a powerful biological weapon that occurs when an individual with augmentations is injected with nanitea but the body rejects them. It then spreads deeper into the cells as the nanites integreate into the cells and spreads deeper and deeper into the virus' host. The virus was deployed by the MJ12 organization ina n effort to have the organization take over the world and the only known cure for it is Ambrosia, a vaccine created by Bob Page and gives it to those who are deemed important.