[jyl]

How does the app know what is an ad and what is not an ad?

I assume the app looks for links back to Google (or whatever company is serving up ads). I also assume that if the ad were served up from the website's own server, the app would not block it. So can't Google simply have the website run some code that fetches ad content from Google, hosts it on the website's own server, forwards a click to the company that placed the ad, and reports the click to Google?

Presumably it might be harder for Google to track users as they move among millions of websites so ads might not be able to follow us from site to site, or be prompted by our browsing, but that's awfully creepy behaviour anyway. If I'm viewing a bike website, I'm okay with seeing context-relevant ads for bike gear, but I don't like seeing ads for diabetic stockings because Google has decided, based on my other browsing history, that I'm diabetic.