There are more than 500 million users affected by in-browser mining. Most of these websites have a shady rep, torrent or adult sites. CoinHive is a better alternative to irritating ads, but since CoinHive can't forbid webmasters from stealth mining, webmasters should ask users permission to drain their CPU resources.

If you have adblocker installed then CoinHive enforces an explicit opt-in, AuthedMine. The AuthedMine miner will not start without an user's consent.

Apart from Adblocker, you can use Chrome extensions like No Coin and minerBlock to block in-browser mining.