The first issue with running a coin miner is using company resources for your own profit. Your own system, using your own electricity, go for it. Running it on a company owned laptop, while at a company building, burning electricity the company is paying for. Ya, that starts to get uncomfortably close to fraud or theft. There is also that whole, "running unauthorized software on a company system, doing who knows what else in the background." There is a very real possibility that the coin miner has unknown vulnerabilities which could allow remote code execution; or, just outright be malicious and contain a remote access trojan. Maybe he was smart enough to audit all the code it was using and be very sure that's not the case. More likely, he just grabbed a random implementation of XMRIG, put his wallet in the config file and ran it. Either way, he also made a point of refusing to remove it, so we escalated up to management. With the recent ransomware outbreak having been in the multi-million dollar (possibly low tens of millions) damage range, refusing to remove unauthorized software went over about as well as a lead balloon. There may have been other factors at play; but, the unauthorized software and being a dick about removing it was what got him out the door.