The stockholm virus is a variant of the xenomorph virus (p. 368, EP) that transforms the mind of the victim before it transforms their body. Stockholm characters view xenomorphs as beautiful and perfect beings and wish to aspire to become them. They become willing allies of xenomorph exsurgents, aiding and concealing them as long as possible. Other exsurgents will not kill stockholm-infected characters but they will ignore or abuse them. Groups of stockholm-infected exsurgents sometimes form cults that seek to create as many xenomorphs as possible.

The long infection time of this virus creates an insidious mechanism to subvert an entire community. Patient zero gradually spreads the virus in a slow and subtle manner. By the time they reach stage 4, others should be infected with stages 2 and 3, allowing them to hide and protect the xenomorph, aided by their psi sleights and obsessive nature. As more of thecommunity becomes infected, more will reach stage 4 and become full xenomorphs. Eventually the uninfected will realize what is going, but by then, there is a full-blown exsurgent cell, with xenomorph shock troops ready to attack. Stockholm exsurgents will also help xenomorphs fight against transhumans, although they prefer to use indirect methods, like deceiving security forces or compromising life support systems. In heavily infected areas, like Earth or the TITAN Quarantine Zone, a stockholm character is a pitiable scavenger, clinging to life, ignored by the gods they worship, but no less dangerous. They may seek to prey upon the empathy of intruders, pretending to be victims who need help, while trying to infect others or alert other exsurgents.

This strain of the virus is harder to detect. Apply a −20 modifier to any detection test until the character reaches stage 4 of the infection.