Cryptojacking is a relatively new threat to the Internet. By the term we refer to websites that exploit the computing resources of their visitors to carry out mining cryptographic coins.
So if it has happened to you that it suddenly slows down computer while the tasks you're doing don't warrant it and your system fans rev up in an attempt to cool the device's components, something's going on… and you've probably fallen victim Cryptojacking. 
That is, someone smart uses your computer resources without informing you…
This is the main issue with cryptojacking: it is done without the knowledge of the users. Various websites load scripts that allow the "smart" page administrator to use your computer resources.
Pages that use such scripts are obviously doing so to generate revenue. One of the advantages of this recently trending feature is that it happens in the background and does not interfere with layout or the content of the website.
Of course there are extensions for browsers that hinder these scripts, but there are others which contain them in a hide and work in the background just like the scripts mentioned above.
Opera Software was the first browser manufacturer to offer protection against Cryptojacking in its browser.
Opera Software engineers have created a site you can visit to check if you are protected by new fashion (Cryptojacking).
Visit just the site and click button Start. The application will test your browser and show you the results, along with the blue button that allows you to download the Opera browser.
Opera Software shows overall test scores on the site, and 74% of all users are protected from Cryptojacking according to statistics data of the page.
Users who use unprotected browsers and do not want to use Opera can install some extension that protects them from Cryptojacking.. They can also use some security software which protects against these scripts. But they can also disable JavaScript on untrusted pages.
