I've been there. It wasn't a virus, but I lost them all - 3rd, 4th & 5th gens. I feel for you. I was so sickened and mad I almost stopped playing... but I was addicted and was back in a day or so. I added some mods to make the game a little different. I don't know why, but making the house and game screens different made me miss my old families a little less.
*hugs*