The long-awaited (and well-reviewed) BioShock Infinite is finally out today. You might be tempted to jump right in to one of the game's three default difficulty settings, but if you crave a classic challenge you can enable it with a little wink-and-nod at a classic gaming reference.
Joystiq reports that by inputting a variation on the Konami Code, you can enable 1999 Mode. The mode's balance is modeled after the classic shooter System Shock 2, which was released in 1999, though we'd like to think the name is also a reference to how Ken Levine is going to party tonight. 1999 Mode is ordinarily unlocked after completing the game, but if you want to test your mettle when going through for the very first time, just input the appropriate code:
Xbox 360: Up, Up, Down, Down, Left, Right, Left, Right, B, A
PC: Up, Up, Down, Down, Left, Right, Left, Right, (Cancel key), (Confirm key)
PlayStation 3: Up, Up, Down, Down, Left, Right, Left, Right, O, X