The latest instalment of the video game Call of Duty has become the fastest-selling entertainment product of all time.Sales of Call of Duty: Modern Warfare 3 hit $1bn (£642m) just 16 days after its release on November 8.The war game broke - by one day - the previous money-making record set by the hit 3D film Avatar in 2009.It notched up $400m (£256m) in sales within 24 hours of its launch date last month.Fans lined up at stores around the world to purchase the military first-person shooter game, the eighth title in the Call of Duty franchise.Eric Hirshberg, chief executive of Activision Publishing, the company which produces the games, said: \"Call of Duty has become that rare entertainment franchise that transcends its own genre.\"Every year, new people are drawn into Call of Duty.\" According to Activision, the war game now has more than 30 million players.Some six million people have registered to play with or against one another online.