X-5
The X-5 Unit supervirus is a highly contagious bioweapon stolen by Dallas and Muddy Grimes in Beavis and Butt-head Do America. Beavis and Butt-head almost doom America to its ravages by accident but then (equally accidentally) save America - obviously good news for Daria Morgendorffer!
It occasionally turns up in Daria fanfics.