MITM attacks. Verizon currently injects tracking headers into HTTP pages.<p><a href="https:&#x2F;&#x2F;www.eff.org&#x2F;deeplinks&#x2F;2014&#x2F;11&#x2F;verizon-x-uidh" rel="nofollow">https:&#x2F;&#x2F;www.eff.org&#x2F;deeplinks&#x2F;2014&#x2F;11&#x2F;verizon-x-uidh</a><p>A variety of ISP&#x27;s (Comcast, MTNL, IDEA) also run MITM attacks and inject ads in pages, sometimes on behalf of law enforcement. I imagine they inject tracking as well.<p><a href="https:&#x2F;&#x2F;blog.ryankearney.com&#x2F;2013&#x2F;01&#x2F;comcast-caught-intercepting-and-altering-your-web-traffic&#x2F;" rel="nofollow">https:&#x2F;&#x2F;blog.ryankearney.com&#x2F;2013&#x2F;01&#x2F;comcast-caught-intercep...</a><p><a href="https:&#x2F;&#x2F;medium.com&#x2F;@sushubh&#x2F;delhi-police-is-literally-doing-a-mitm-attack-on-all-mtnl-broadband-subscribers-in-delhi-these-days-e26e4d673e50" rel="nofollow">https:&#x2F;&#x2F;medium.com&#x2F;@sushubh&#x2F;delhi-police-is-literally-doing-...</a><p>Google could either do these things or block others from doing them.