The Mind Virus is a version of the Unity's FEV designed to wipe the individual's memory of the horrors of becoming a super mutant.
Background[]
After the Unity collapsed, the Master's Army remnants fled Angel's Boneyard, leaving behind a few barrels of FEV. This strain of FEV would seep into the water table, and begin tainting the minds of those who drank the water or encountered it on land, no longer susceptible to diluting when exposed to air as the original and Master's strain had.
One such encounter was described by the wasteland scouts on a mission to a California tribe camp known as Xiabula, in which the inhabitants there had been attempting to work on a cure for the virus. Rossman then took it upon himself to install a hologram projector in a nearby vault in order to monitor and purify the water supply of Mind Virus, as well as vaccinate Californian tribals and those who might become infected with the Mind Virus.
Mercenaries at the NCR prospecting company Nova Star tracked him and poured more Mind Virus into the water supply. While the effects weren't substantial, the number of California tribe members infected has become a threat for travelers who remain uninfected, and a death sentence to the few uninfected Californian tribals.
Roleplay Note[]
Star player is designed to, possibly, get infected with Mind Virus. Dialog, both voice and text, indicate positively that after get infected and losing wit wandering the desert, Star did "gnaw the bone of your enemies". Non-cannibalism players are forewarned to avoid getting infected in order to stay out of this certain outcome. While in some versions there's a chance of getting to Xiabula before the Mind Virus hit in full force, it's chancy enough that a strong anti-cannibalism player should take great care in dealing with Euripides' infected savages (who have scripts to force this event). The infected savages outside of Xiabula and Altar of the Ghost dont seem to have these scripts.
Appearances[]
The Mind Virus is mentioned in Fallout: New California.