Borg
Species 6339 developed a synthetic pathogen so that when they were assimilated by the Borg, so that it would be spread to the Borg vinculum. From there, it caused all drones within range to experience the Borg equivalent of multiple personality disorder, eventually leading to their self-destruction. The process would be repeated when another Borg vessel retrieved the vinculum, and so on in "Infinate Regress",