In-browser cryptocurrency mining market has become incredibly crowded. New sites that offer similar services are popping up on a weekly basis. Most are behaving like malware, intruding on users’ computers and using resources without permission. Microsoft spotted two new services called CoinBlind and CoinNebula, both offering similar in-browser mining services. None of these services even have a homepage, revealing their true intentions to be deployed in questionable scenarios. In-Browser miners are usually deployed on questionable websites, such as piracy portals, illegal streaming services, adult portals, and others.
Source: https://www.bleepingcomputer.com/news/security/the-internet-is-rife-with-in-browser-miners-and-its-getting-worse-each-day/