For convenience, I had Dumbledore say to Harry, "You were the Horcrux he never meant to make." But I think, by definition, a Horcrux has to be made intentionally. So, because Voldemort never went through the grotesque process that I imagined creates a Horcrux, with Harry, it was just that he had destabilized his soul so much that it split when he was hit by the back-firing curse. And so this part of it flies off and attaches to the only living thing in the room. A part of it flees in the very close-to-death limbo state that Voldemort then goes on and exists in. I suppose it's very close to being a Horcrux. But Harry was not-- did not become an evil object.
-- J.K. Rowling (PC-JKR1)
Harry Potter receives a scar on his forehead when the curse rebounds off of him. Voldemort’s body is destroyed in the blast and a piece of his soul attaches itself to the only living thing in the room: one-year-old Harry Potter. While not becoming an actual Horcrux, Harry functions very much as if he is one, harboring the bit of the Dark Lord’s soul for many years.