Today unfortunately, I have suffered the same issue. I was using my phone all morning sitting in my car at school. Walked to/from a building in ~30 degree weather to a nice warm car, and drove home. Later, when I looked at the screen it looked like a hair or spiderweb was on the screen. I rubbed it, and nope, it's real. The crack is UNDERNEATH the glass, and my phone is absolutely flawless. I've had it for only four months and there isn't a scratch on it. Going to call Samsung tomorrow and be prepared to bend ov.. I mean, hope they fix it. I will take pictures tomorrow and upload them with an edit to this post.
Edit 1: I forgot to add that the phone is still operating fine, with no issues or change in functionality. If you look directly at the screen the crack can't be seen, its only when you tilt it around you can see the it.