"You are now connected to a shared network"? I am one computer how is it I am 'shared'?

Norton Internet Security popped up a window and told me, "You are now connected to a shared network." ???  I am only one lap top connected via an AT&T router as they are my ISP.  How is it Norton is stating I am connected to a 'shared' network and how to validate this statement by checking.  netsh commands?  Ipconfig commands?  What may help with this -- I am too knew to 'behind the scenes' of computers and need some help on learning to check and what and how to check to learn about this.  Any help is appreciated.