http://www.joystiq.com/2013/03/25/unlock-bioshock-i...the-konami-code/ By default, Infinite only has three available difficulty settings: Easy, medium and hard, with the 1999 Mode – which tunes Irrational's latest game to a difficulty best suited for those looking for a classic shooter experience akin to System Shock 2's campaign – hidden away until the game is complete. If players decide they want an immediate challenge, using the Konami code will allow them to unlock it at any point.
On PC (with keyboardmouse): Up, Up, Down, Down, Left, Right, Left, Right, (Cancel key), (Confirm key)