Reality Benders: Countdown by Michael Atamanov

At long last, an extraterrestrial civilization reached out and made the First Contact. However, no one on Earth took their communique for the genuine article. In a similar vein, very few people appreciated just how little time our new suzerains had promised to keep our planet safe. Regardless, the end of their message showed humankind how to access a mysterious game. The objective of this game is unclear. No one can say where its servers are located, and its inner workings are beyond comprehension. But the game slowly gained momentum, pulling in more and more players. Soon enough, it became impossible to ignore the fact that things that happened in the game had a direct impact on our reality. And not only ours...But as people figure out this mysterious game, the countdown timer ticks away. And no one can say exactly what will happen when Earth's safety is no longer guaranteed.