The artificially created disease was a mutagenic virus that was created by the rogue Vulcan scientist T'Uerell who created it using Borg knowledge from the civilizations that the Borg Collective had assimilated. It was the outcome of an alliance made between T'Uerell and the Romulan's; the latter provided her with Protomatter as part of the exchange.
Once created, the toxin was manufactured in liquid form on a number of harvesting stations within Romulan territory and was deployed through drone ships onto target worlds. Planets such as Enkaria and the worlds in the Epsilon Theta system were infected by the toxin with the former being cleansed of life by the disease. The Enterprise was responsible for destroying the Romulan manufacturing centres which prevented any new quantities of the poison from being created.
However, the Romulans had three drone ships with the disease and attempted to storm the United Earth's defense lines in order to deploy it on Earth itself. It was only a successful defense by the United Earth Starfleet prevented the Romulans from accomplishing their goal. In the aftermath of the attack, scientists began working on a counteragent for the bioweapon to treat those worlds that had been infected by it. (ST video game: Legacy (game))
- The disease was not given a formal name within the game and was referred to as the "Toxin", "Disease" and as a "mutagenic virus".