Cryptojacking is a relatively new threat on the Internet. The term refers to websites that exploit the computing resources of their visitors to mine cryptocurrencies.
So if you have ever had your computer suddenly slow down, while the tasks you are doing do not justify it and your system fans speed up in an attempt to cool the device's components, something is going on... and you have probably fallen victim to Cryptojacking. 
That is, someone clever is using your computer's resources without informing you...
This is the main issue with cryptojacking: it happens without the knowledge of the users. Various websites load scripts that allow the use of your computer's resources by the "smart" administrator of the page.
The pages that use such scripts, obviously, do so to generate revenue. One of the advantages of this operation that is becoming fashionable lately is that it happens in the background and does not interfere with the layout or content of the website.
Of course, there are browser extensions that block these scripts, but there are also others that contain them carefully hidden and work in the background just like the scripts we mentioned above.
Opera Software was the first browser company to offer a guarantee of protection against Cryptojacking in its browser.
Opera Software engineers have created a website that you can visit to check if you are protected from the new trend (Cryptojacking).
visit the website and click the Start button. 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 displays overall test scores on the website, and 74% of all users are protected from Cryptojacking according to the statistics on the page.
Users who use unprotected browsers and do not want to use Opera can install an extension that protects them from Cryptojacking. They can also use security software that protects against these scripts. But they can also disable JavaScript on untrusted pages.
