Comcast has begun serving Comcast ads to devices connected to one of its 3.5 million publicly accessible Wi-Fi hotspots across the US. Comcast’s decision to inject data into websites raises security concerns and arguably cuts to the core of the ongoing net neutrality debate. A Comcast spokesman told Ars the program began months ago. One facet of it is designed to alert consumers that they are connected to Comcast’s Xfinity service. Other ads remind Web surfers to download Xfinity apps, Comcast spokesman Charlie Douglas told Ars in telephone interviews. Continue reading this story here.