My ISP makes me use a "gateway"[1][2] with a wireless router built into it. In the name of reducing electricity usage, I forego running my own router and surrender to using theirs. I would be willing to bet many others do the same. I wonder how secure it is?
[1]http://www.att.com/u-verse/explore/residential-gateway.jsp [2]http://verrytechnical.com/wp-content/uploads/2011/10/ATTUver...