This tool was designed as an alternative revenue-gathering method for website admin, who are looking to get rid of unwanted ads, taking all the space in their webite. Even though, this tool help to mine Monero (cryptocurrency), which is less valuable than BitCoins, but still, its in the top 10 cryptocurrency in the world.
HOW TO PREVENT IT
It may not be very lucrative when used on small websites, but imagine a Coinhive miner on every Facebook and Google page? It could happen.