Novel about a computer game with secrecy

Question

This is a young adult novel I read within the last 5 years, but I can't say it was new at the time.

(what I remember) Near future. The main character is a high-school boy. There is a new computer game. But you cannot buy it. Someone gives you a disk with the game copied onto it. But you have to agree to conditions: you will play only in private; you will not reveal outside the game anything that happens inside the game... After you play a while, the game starts to ask you do perform some seemingly meaningless tasks in the real world. Most of the time we, the readers, are trying to figure out what is going on: is there something sinister behind this game?

Obviously I remember this book. But I do not remember the title. What is it?

Answer 1

(Answering my own question.)

Erebos by Ursula Poznanski
published 2010 in German; English translation, 2012

From the Amazon description:

When 16-year-old Nick receives a package containing the mysterious computer game Erebos, he wonders if it will explain the behavior of his classmates, who have been secretive lately. Players of the game must obey strict rules: always play alone, never talk about the game, and never tell anyone your nickname. Curious, Nick joins the game and quickly becomes addicted. But Erebos knows a lot about the players and begins to manipulate their lives. When it sends Nick on a deadly assignment, he refuses and is banished from the game. Now unable to play, Nick turns to a friend for help in finding out who controls the game. The two set off on a dangerous mission in which the border between reality and the virtual world begins to blur. This utterly convincing and suspenseful thriller originated in Germany, where it has become a runaway bestseller.