This game.
This game is scary, through and through, you'll be unsettled from the start...
When you first start the game, there's a simple task, but once you've completed it (when it ends.) it creates files on your computer, compelling you to play again... but it only gets worse, the game changes, it gets scarier, it will change itself for the worst if you don't save yourself and complete it all...
I
order you to play this game, it's great, especially with the changing files thing - which is in no way harmful, and won't do anything dramatic (Well, only to its own folder...).
http://www.moddb.com/games/imscared-a-pixelated-nightmare