Not too long ago the four player coop craze had taken PC's and Consoles on fire and all we wanted to do was kill zombies and pull of heists with our buddies. What if, Overkill and Valve said to themselves, we created a cross over title between the two games? Well, we know that it is happening but no details with regards to what we can expect, except that the game will have an 'infectious' story. Well, we'll take it.