Gray Death

The Gray Death is a nano-virus used by Majestic-12 in the game Deus Ex as part of their plan to take over the world.

Design
The Gray Death occurs when an individual without a predisposition for nanoaugmentation is infected with nanites. The nanites integrate themselves into the individual's cells and the individual's body rejects the nanites, and by extension the cells that the nanites have integrated with. The virus can be halted by the use of Ambrosia, a vaccine that consists of ROM modules which attach to the nanites. The virus and vaccine both must be manufactured in a Universal Constructor.

The nanites were originally created by Morgan Everett, also noted that Megan Reed had a hand in it as well. but the idea to use them as a weapon was first put forth by Bob Page, which was frowned upon and caused Bob Page to form the splinter faction, Majestic 12.

Use
Both the Gray Death and its vaccine, Ambrosia, are produced by VersaLife, a subsidiary of Page Industries. By creating large amounts of Gray Death and small amounts of Ambrosia, MJ-12 were able to force important individuals to perform their bidding. For example, Bob Page placed an unnamed senator on the priority list for the vaccine in exchange for promoting Walton Simons to position of director of FEMA. MJ12 also used the virus to create a state of emergency and generally destabilize the world.

There is also indication that the release of the virus was intended to speed up the nanoaugmentation project. MJ12 had Ford Schick, a scientist they captured in New York, working to integrate the Gray Death into test subjects. If Schick, or any other scientist, were to find a way to eliminate the negative health effects of the Gray Death they would discover how to successfully nanoaugment anyone in the process.

Bob Page hints towards the end of the game that any cure will be ineffective as he can simply change the Gray Death architecture using a high prime number to "encrypt" the virus. This could be interpreted as Page becoming desperate. Your turn. Desperate.

Desperate.

Trivia
In Human Revolution, while in Detroit at the time of the riots, a hobo can be heard zealously preaching to others, one of his lines being that "Death is coming, gray and deadly", a clear reference to the Gray Death which runs rampant two decades later during the events of the original Deus Ex.