1. Ad networks/exchanges allow ads to run arbitrary JS and try to rely on "catching" bad ads instead of properly restricting what ads can do. 2. Publishers tol

1. Ad networks/exchanges allow ads to run arbitrary JS and try to rely on "catching" bad ads instead of properly restricting what ads can do. 2. Publishers tolerate this and use such ad networks. 3. Browsers do what they're supposed to do, execute the code delivered by the publisher's site and the resources it references. The only thing browsers could do is show a warning that "www.publisher.example.com is using large amounts of CPU resources" to discourage web sites from being shitty, but ultimately, it's the responsibility of the publisher to make sure his site doesn't serve malware. Keep in mind that next time, it could be a 0day exploiting your browser instead of a miner.