David Kravets reporting on Comcast injecting ads on top of webpages when connected to their public wifi hotspots:
“We think it's a courtesy, and it helps address some concerns that people might not be absolutely sure they're on a hotspot from Comcast,” Douglas said.
Now they will know, and can promptly make the wise decision to get the hell off your wifi.
These unwanted JavaScript injections are terrible. I've been told serving your site over SSL can stop this, which is why (in part) I serve this site over SSL. (Even though it is tremendously slower.)