Cognitive Fragmentation Disorder (CFD) is a personality disorder caused by nanites. The nanites "overwrite" the victim's personality with that of an AI. Victims of CFD (or at least the AIs) refer to themselves as "monads"; while the more derogatory term, "headcase" has become popular in the shadow communities.
In 2072, Fastjack, Riser, and an unnamed team of runners hit Celedyr's Albuquerque Lair for a run. At this point the team becomes infected with CFD and maybe the first known CFD victims. Fastjack tells Riser to kill the rest of the team.
In 2073, Miles Lanier suspects Celedyr is hiding something, so hires runners to infiltrate Transys Neuronet facility in Wales that's conducting Project Imago research. Celedyr moves his research to his Albuquerque Lair after the events of that run.
In 2074, Evo's Mars base, Gagarin, goes offline due to a CFD outbreak. At this point, the CEO of Evo, Anatoly Kirilenko goes missing in space for months and becomes infected with CFD on a return trip from Gagarin. Towards the end of the year Miles Lanier releases a file to Jackpoint detailing the symptoms of CFD and Fastjack reveals his infection and retirement from Jackpoint.
June 2076, Pax betrays Celedyr and attempts to upload Deus in to an experimental dragon variant of CFD to take control of Eliohann's body. Cerberus realizing something is wrong loads himself as well and they end up creating a new AI called Cerius, while possibly still keeping themselves as two individuals. From there, the infected Eliohann breaks free from the MIT&T facility where the experiment was being conducted, and attempts to attack NeoNET Towers in downtown Boston. They are immediately repelled by Celedyr and crash in to Fenway Park and afterword fly north towards Salem. The next day all of Boston is locked down by a multi megacorp task force to prevent anyone from entering or leaving the city. The city itself is thrown in to anarchy, much like Bug City, as many people become zombie-like headcases.
2077, the CFD sufferers announce their presence to the Corporate Court and call themselves Monads. They announce plans for Project Exodus, to take all the CFD infected into deep space and leave the solar system by 2080.
Nanites that are used for nonorganic use such as those used in Nanoforges for 3D printing, often fail as the nanites are reprogrammed.
Nanites inside a metahuman will attempt to infect and reprogram or just destroy uninfected nanites. The nanites are reprogrammed to also reproduce by Replicator nanites, which are only found inside victims of CFD. Soft nanites use natural organic material found in the body. Hard nanites will compel the host to eat non-organic material, such as metal or sand, to give the hard nanites material to build new hard nanites.
The host will often suffer from lapse in memory or blackouts. During these lapses the AI personality often takes over the host and works on furthering their own agenda. Sometimes the two (or more) personalities will not be aware of each other's existence.
If a host is infected with nanites containing a different AI personality, the different nanites will attempt to fight each other for control of the host. It is also possible for a new personality to be overwritten with another personality. If multiple nanite personalities are attempting to imprint on the same host, they will often end up creating a new hybrid personality which is an amalgamation of the different personalities in the host. Infecting a host with nanites from a different subject but with the same personality causes no conflict.
Celedyr has created non-wireless hunter killer nanites to combat CFD nanites called Overwriters. By 2079 they are a reliable way to combat minor infection.
Shiawase has created a process called NanoScrub, which can take several hours to administer and has side effects on some cyberware, but is more effective at combating higher volume of nanite infection.
It is possible to do Matrix combat and kill the AI personality, however it requires entering a Foundation-like Matrix construct formed from the distributed network of all the nanites.
FastJack has created a program that is able to put the AI personality in to a dormant state inside the host body. It is however not 100% reliable as it is possible for the AI to free themselves at inopportune times.