According to a report published by McAfee in June,
"The McAfee Labs count of total coin miner malware rose by 629% in Q1, to more than 2.9 million samples."
For the report visit
https://www.mcafee.com/enterprise/en-us/assets/reports/rp-quarterly-threats-jun-2018.pdf
For an article about the report visit
https://www.bankinfosecurity.com/cryptojacking-displaces-ransomware-as-top-malware-threat-a-11165