A nanovirus, also known as a nanokiller, was a selective virus designed to kill only an individual or specific groups of people that it had been developed to, without harming other undesired individuals.
Nanoviruses targeting specific beings or groups of beings were notoriously difficult to produce due to the need of identifying an entire genome, or else the virus would not attack the target. Routine natural mutation, interbreeding, and genetic engineering would make an individual immune to the virus's effects. This weakness could be skirted by having the virus target a specific, unchanging gene sequence that would make its target or targets stand out from the larger population such as the one used to increase the rate of aging within clone troopers. More dangerously, a nanovirus could be keyed less specifically in order to kill subjects of an entire race, such as humans, indiscriminately.
One example of a nanovirus was the FG36 virus, under development at the start of the Clone Wars by the Separatist-aligned Doctor Ovolot Qail Uthan. FG36 was specifically engineered to target the Fett genome present in the Grand Army of the Republic's clone troopers. Uthan and her scientific team were sent to a secret lab on the remote planet of Qiilura to carry out their work. However, before development of the virus could be completed, Uthan was captured by the clone commandos of Omega Squad and brought into Republic custody. The lab was destroyed and development of the virus presumably halted; Supreme Chancellor Palpatine, however, kept the unfinished nanovirus and Uthan was held on Coruscant as part of a back-up plan for stopping the clone troopers, should they ever turned on him. After the formation of the Galactic Empire, Palpatine used FG36 on Uthan's home planet of Gibad, killing all sentient life on the planet. Because of this and the danger the virus continued to pose, Uthan—having been rescued from her incarceration at the Valorum Center by Mandalorian Kal Skirata and his associates—developed an antigen to immunize against FG36. The completed antigen was spread first to Skirata's clan and across Mandalore, and then to the Jedi community of Master Djinn Altis.
A variant of the nanovirus was used on Mon Mothma during negotiations with Furgan, the ambassador for the Caridan system. He brought his own drinks with the real drink on one hip, the nanovirus on the other. The nanovirus was made to kill her slowly, and make it look as if the Rebellion was dying, being bureaucratized by the New Republic. It did not kill her, because Carida lost control over Terpfen, who immediately told what happened to the New Republic on the toxin. Then, Cilghal, a Jedi Learner at that time, healed her by removing the nanovirus particles from her.
A variant of the FG36 virus was later developed by the Imperial Remnant's Council of Moffs during the time of the Second Galactic Civil War. It was first used during the Battle of Roche, where it specifically targeted the Verpine soldier caste, while leaving other Verpine unharmed. Soon after, the virus was developed to target the Hapan Royal House, and another strain to target Boba Fett and any other member of the Fett genome was deployed on Mandalore. However, the effectiveness of the Mandalore-deployed nanovirus was questionable, due to the cure to the baseline virus that had been spread across the world decades prior, in the weeks following the Clone Wars. Despite doubts as to its effectiveness, by 45 ABY, the nanovirus had prevented Fett's offspring from returning to Mandalore, specifically Mirta Gev, who worked to find a cure to the nanovirus. In her efforts to find a cure, she allied her Mandalorian soldiers to the Columi brothers, Craitheus and Marvid Qreph who agreed to help develop a cure. However, the Qrephs either refused or were unable to develop a cure, leaving the offspring of Fett to find another way to cure the nanovirus and be able to return to Mandalore.
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- "The Zombies of the Galaxy" — Star Wars - The Official Magazine 95