Hackers are able to use your CPU towards their hashing power in order to mine a cryptocurrency, in this case, Monero. Browser-based mining is not to be confused with file-based mining, which is when a dedicated executable file is downloaded and ran.
Overtime, such mining can generate a significant amount of revenue. While browser-based mining is nothing new (first seen in 2011), the rise in the cryptocurrency market has likely led to its new found glory.
This form of “covert” mining ceases when the visitor leaves a site or closes the window…until now. Such a feat is possible through the use of a pop-up window that is hidden behind the Microsoft Windows taskbar. Mining will stop when the user closes the pop-up window.
Even the “big guys” can fall victim to browser-based mining.
A Starbucks store in Argentina mined Monero through its customers in December of this year. As a result, Starbucks customers experienced a ten second delay when connecting to the store’s wifi. The JavaScript came from CoinHive, a tool that allows website owners to gain revenue by mining Monero in customers’ browsers.
Two of Showtime’s websites (showtime.com and showtimeanytime.com) had a script running that utilized viewers’ CPU to mine Monero in September. Comments in the code suggested that the originator was New Relic, a web analytics firm, but they have denied their involvement in the matter.
Like Showtime, CoinHive’s JavaScript was also found on Safebrowser, a Google Chrome extension. Research suggests the authors of this extension chose to implement the code in their product.
Sources: Symantec, Bleeping Computer, ars Technica, Cryptovest, Gizmodo, Extreme Tech
Legitimate websites use Coinhive to generate revenue without ads.
You are correct, although not all customers are thrilled with this.