Simplify the following text for a Grade 4 native English-speaking person.
Original: By June 20 , 2006 , more than 500 million games of Halo 2 had been played and more than 710 million hours have been spent playing it on Xbox Live ; by May 9 , 2007 , this number had risen to more than five million unique players .
Simplified: By June 20 2006 over 500 million games of Halo 2 had been played over Xbox Live .