Erebos

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.