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Google, Cloudflare & Cisco Will Poison DNS to Stop Piracy Block Circumvention * TorrentFreak
(torrentfreak.com)
This is a most excellent place for technology news and articles.
How is that even legal?
It is legal just only because they can restrict the access to any of the services they want, in fact they don't oblige you to use their DNS...
How would it be illegal? It's their service, they can set whatever rules they want on it. If you don't like it, pick another DNS provider.