"Guitar Hero II" is a music video game developed by Harmonix and distributed by RedOctane, and is a sequel to "Guitar Hero". The game was released first to PlayStation 2 in 2006, but later released for the Xbox 360 in 2007. "Guitar Hero II" challenges players to recreate the lead guitar portions of many rock music songs using a specially designed guitar-shaped controller, based on either a Gibson SG for the PlayStation 2 version, a Gibson Explorer for the Xbox 360 version, or else a standard console controller. As notes scroll down the screen towards the player, the player must hit both the fret buttons on the guitar controller and the strum bar at the same time to successfully hit the notes. Successfully hitting notes improves the player's performance in the game and also raises their score, while missing notes will reduce the player's performance, and a poor performance may end the song prematurely. Each song can be played at one of four difficulty levels: Easy, Medium, Hard and Expert. These levels reflect the number of fret buttons used and the number and frequency of the notes to be performed.