 Overall , the Guitar Hero series has sold more than 25 million units worldwide , earning US $ 2 billion at retail . Activision claimed the series to be the 3rd largest game franchise in 2009 after the Mario and Madden NFL franchises . 
 Overall , the Guitar Hero series <a href='been_done' title='1'><mark>has</mark></a> sold more than 25 million units worldwide , earning US $ 2 billion at retail . Activision claimed the series to be the 3rd largest game franchise in 2009 after the Mario and Madden NFL franchises . 
Overall , da Guitar Hero series done sold more den 25 million units worldwide , earning US $ 2 billion at retail . Activision claimed tdaseries to be thdard largest game franchise in 2009 after thedario and Madden NFL franchises .