“So, what are you working on at Umbrella, Jeff? A new type of bread that stays fresh longer? A more fuel-efficient car? No? Oh, you’re working on a weaponised virus? One that could wipe out mankind if it gets into the wrong hands? I foresee no problems with that, Jeff. No, sir.”
As is the law, when it comes to Hollywood and video games, the worst case scenario happens: in this instance, the T-virus is exposed to the population of Raccoon City (and later, many other places around the globe), turning them into aggressive zombies. The solution, as played out in Resi 2, is to nuke the whole city. See, if Umbrella had been researching new flavours of ice-cream, this never would have happened.