JSE Coin and Coinhive allow webmasters to install coin miners into their websites as an alternative means of monetization. The most notable platforms that provide JavaScript cryptocurrency miners for websites are JSE Coins and CoinHive.com. These platforms allow webmaster to register and obtain a snippet of JavaScript code that they can install on their sites. This code will work in the background of visitors browsers, mining coins by utilizing excess CPU power of their computer. Its a natural move for bad actors who similarly abuse other legitimate means of website monetization, for example, installing their own ad or affiliate codes to third-party sites.”]
Source: https://blog.sucuri.net/2017/09/hacked-websites-mine-crypocurrencies.html