The trouble is, websites and malicious code are using our computers to mine cryptocurrency without our knowledge. We pay for the electricity and contend with a slow computer but get none of the benefit from it. According to the piece from Adguard linked above, 500 million computers are being used to mine cryptocurrency without their owners even being aware.
Some of the websites that feature cryptojacking code profess no knowledge of it. Given the anonymous nature of cryptocurrency, we have to take their word for it. There is a quick and easy way to tell if a particular website uses cryptojacking code. If your CPU utilization spikes on a particular website or page, go to a different page. If utilization drops, it is a good indication that it is cryptojacking you. You could also shut down your browser as a double check. While not as dangerous as malware or a virus, cryptojacking is still using your computer for someone else’s gain. That is not acceptable and we need to do something about that.