I have recently started using tethering through an android phone for internet access.
Connection triggers nmcheck.gnome.org, which I understand is something to do with connectivity facilitation through Network Manager, per this question Some supisious software making request to nmcheck.gnome.org
Fine. Except, I seem also to be receiving an ad attached to the nmcheck response screen. Not fine.
Where is this ad coming from? Is it my ISP intercepting the http traffic? How do I stop this?
Edit:
I have looked at a tcpdump of the traffic on port 80 during the connection process. I see connections to
- the mobile ISP
- Red Hat, the host of gnome.org
- a cloud provider, which I think may provide a gateway service for the ISP.
It's probably your ISP injecting the ad, yes. I do not see it, and I've checked from a couple of locations.
There would be no reason for the gnome project to inject ads there. First of all, it's not meant to ever be seen by a human, so no-one would ever see the ad, rendering it ineffective.
Second, the Gnome project doesn't appear to have advertising at all on their pages. They load no javascript external to gnome.org as far as I can tell. The hosting is provided, as you say, by Red Hat.
To stop this, you can either use a VPN connection, or petition your ISP to stop this stupid behavior.