Coinhive was an in-browsing Monero mining service that allowed websites to inject JavaScript code into websites to mine Monero using a visitor’s browser and CPU. CoinHive was used legitimately in a few cases, such as to raise money for charity, but the majority of times, it was used to illegally mine cryptocurrency without a user’s permission. Have I Been Pwned’s Troy Hunt has taken over the domains for free as long as he would do something useful with them.
Source: https://www.bleepingcomputer.com/news/security/coinhive-domain-repurposed-to-warn-visitors-of-hacked-sites-routers/