I keep seeing an SSID called "Hidden network" everywhere, why is this?

All this means is that your computer sees a wireless broadcast that is not presenting a SSID. If you were to attempt to use it the first thing your connection wizard will ask for is the SSID which you would input. Then it would ask your for the security information like typical wireless connections. You will see these in many different places. Nothing to be bothered by.

Some use it as they think it makes them more secure when in reality it is security through obscurity. I have one connection like that in my house for some of my inferior devices that cant support higher levels of encryption.

New routers from Verizon and Xfinity have a "Hidden Network" as part of a new initiative to boost speeds without installing actual infrastructure. It's a new way to extend signal to hard to reach places like the rural midwest where 1 tower is enough to supply a whole zip code by bouncing signal off routers in the neighborhood. To get rid of this "HIdden Network" you have to log into your Verizon, or Comcast account and Opt Out. You can do so in your account or call customer service. Someone from technical support will access your router, stop the Hidden Network, and you should see a small boost of 30mb in performance from your router.

Here are some additional information about what's happening.

http://uproxx.com/technology/comcast-makes-customer-routers-public-wifi-points/

http://www.cnet.com/news/comcast-expands-wi-fi-network-with-new-neighborhood-initiative/