Nanites

From DeusEx Wiki

Nanites are tiny robots (measured on the nanoscale; 1 nanometer is one billionth of a meter and ten millionth of a centimeter) that travel through the human blood stream.

Nanites are used in the Deus Ex world for a variety of purposes, ranging from minor tasks, such as teeth-cleaning, to intensive purposes such as nano-augmentation. In Deus Ex, nanites are responsible for the Gray Death plague. In Deus Ex: Invisible War, airborne nanites turn deadly in Cairo, bringing about a nanite plague; whoever breathed them in would be killed internally. In the endgame, if the player chooses the ApostleCorp ending, nanites are used to distribute biomod infusions worldwide.