two students at goucher college the game humans versus zombies simulates a zombie apocalypse and is growing in popularity at colleges across the nation. over 900 players participated in this september's game at the university of florida. >> i think people are looking in a variety of ways for escapist entertainment, escapist enjoyment. >> reporter: here are the rules. first and foremost, these players must use nerf guns that are brightly colored and cannot be seen inside buildings on campus. but once the missions begin and we're out here in the open, there's no stopping these players from getting violent. the game has recently come under scrutiny for security reasons. at the university of pittsburgh at greensburg the game has been altogether banned. humans versus zombies even prompted a lockdown in 2009 at alfred university after the tip of a nerf gun poking out of a student's pocket was mistaken for a real one. >> nerf guns, you can't hurt