Those that virtually "hunt" and "gather" all necessary virtual Big Mac ingredients (six in all) will be rewarded with a free actual Big Mac.
The various QR codes can be found in restaurants, online, on outdoor advertising, and on TV. Duplicate codes can be traded with other players. Once a set of all six are collected, players can take the phone to McDonald's to redeem for a Big Mac.
Here's a video explaining/promoting the game (it's in German, of course):
