The key developer of NiceHash, Matjaž Škorjanc, is a known black hat hacker who has done prison time for creating malware
"Computer crime-fighting authorities were successful at bringing down the Mariposa botnet at the end of 2009. But at its height, the botnet (named after the Spanish word for "butterfly") had silently compromised and hijacked almost 13 million computers in more than 190 countries.
The polymorphic malware behind the Mariposa botnet was Rimecud, which spread between computers using a variety of methods - includingcopying itself to removable storage devices, instant messaging and P2P file-sharing systems.
Once infected, compromised computers were recruited into the botnet, and operators could steal information including passwords and credit card details from victims."
https://www.grahamcluley.com/mariposa-botnet-mastermind-receives-almost-five-year-prison-sentence/