Fans have discovered a URL in the first trailer for The Amazing Spider-Man 2 that leads to a viral site for the film called Electro Arrives, and it shows Harry Osborn looking over a computer screen with a countdown to something that will happen 19 days from now. Obviously it has something to do with Electro, but what? Maybe another trailer that focuses on Electro? I guess we'll eventually find out!
My best guess is that it's a countdown to the new footage that will be shown at New York City's Times Square on New Year's Eve. It makes sense that they would release it online simultaneously.