Hacker gangs are raking in millions of dollars using a technique called cryptojacking. It works by illicitly harnessing the computer power of thousands of people to mine cryptocurrency without them knowing .

Guillermo Suarez-Tangil at King’s College London and Sergio Pastrana at Madrid’s Carlos III University analysed more than 4.4 million malware samples that were used for cryptojacking between 2007 and 2018.

The pair found cryptojacking had generated an estimated $57 million worldwide since 2007, with the top-earning gang minting $18 million worth of cryptocurrency …