The Krytos virus was a dangerous alien only bioweapon developed by the Galactic Empire and released on Coruscant after the New Republic liberated the planet. The virus could only be cured with Bacta. And the only planet that could produce it, Thryffa (I think that I spelled that right); was still under Imperial control. And they shut down the mass export of bacta. Which led to what became the Bacta War and the liberation of the planet. By the time the virus was dealt with, millions of aliens had died.