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Google tries to defend its Web Environment Integrity
(techreport.com)
This is a most excellent place for technology news and articles.
No, but that only works if the ads are being served by known ad hosts, so you should expect that adtech will get hip to that and proxy their traffic through the same hosts as the content.
That being said, it’s pretty easy to check if a user has network blackholing going on in clientside JavaScript, you just do a test request to a popular ad network and see if it resolves, no special browser support needed.