Anyone who deals with cryptocurrencies knows that mining requires very powerful systems. So if you are thinking of pursuing a "sport" you must first invest in a very good computer system. 
Recently some websites have started to use pconditions of the system of the users who visit them, for mining. Some of them display on the screen a notice that explains what will happen before it starts, while others start using your system without mentioning anything.
This publication refers to the second sites, which are starting to use the resources of their visitors' systems to gain cryprobes.
Who is mining? is a web application that has a comprehensive list of all known mining websites. It also allows you to check out a mining page without telling it to the end user.
Visit it whoismining.com and type the URL of the page that you suspect uses your browser to do mining cloaking. The web application will confirm whether your suspicions are true.
The app still has endless lists of webpages with that behavior.
If you see that a page you are interested in uses your computer, you can simply stop visiting it. If you can not again without it, you can block mining from your browser with an add-on or extension.
It's worth debating whether or not this practice is right, especially when sites choose not to reveal what they're doing. Some users of these pages have not problem to allow their system to be used for mining encryption, however it should be up to the user to decide if they want to do it or not.
