I occasionally get a menu invitation for a new Net hookup. What is this?

I get my internet from Communicom on cable, and somethings after I get this msg asking if I want to join this new computer net and I refuse, my internet goes out.
There is already one Net and I don’t know if that connects me to my server or what.
I’m sure the FBI and Big Brother are everywhere, anyway, but what would you do?
PS Bad News is that they’ve extended the Patriot Act another 3 months…