Without reading the other posts, I'm going to blindly step in here...
At my school, routers are allowed, but not wireless. I go to a tech school, so people may have multiple computers, networked printers, game consoles, etc, so there's a reason why a lot of kids have routers. I have one in my room because my roommate and I both have iPhones and have apps that sync. We also both have wireless printres. Even with clever naming, an unbroadcasted SSID, and encryption, they managed to find out that my room had a wireless router. How did they do this? I have no idea... I'm actually applying for a position at the office that provides telecommunications services to my school, so maybe I'll find out, but they have their ways.
And if they do figure out it was you, the consequences can go from a warning to having your room's internet revoked. And yes, they can and may do that.