CoinHive miners can be injected into compromised sites without the consent of the website owners. Old version of the miner is gaining popularity with hackers as it allows them to keep the injected miner below the radar. The old version does not require an opt-in. It can work silently on websites that use it. Some sites add the miner without removing any other ad scripts from their player iframes. The miner can be used silently by websites who neglect user experience and only care about profit to keep using it.”]
Source: https://blog.sucuri.net/2017/10/cryptominers-on-hacked-sites-part-2.html