What’s the damage?

How much of a problem can the hidden miners be for end users? If websites or apps don’t throttle the CPU usage, the strain on hardware can be dramatic.

“This was not sustainable for long periods of time,” said Bitfalls editor Bruno Škvorc, who implemented an early version of the technology on its site ( “Someone reading a post for ten minutes would have 5% of their battery eaten at 40% mining efficiency.

“That’s a lot, and most other sites didn’t even stop at 40%, they went to 90%+. We used 20% and informed people in advance, and gave them the option to opt out.”

When PC Pro ran the hashing process at 100% efficiency from the Coinhive website, CPU usage jumped from 4% to 89%.

For Bitfalls, not only did early efforts drain battery from mobile devices, but a flurry of warnings from onboard security software and negative media coverage also meant the minimal profits for the publisher were not worth the bad publicity. “Those who heard about it from mainstream media were understandably scared,” said Škvorc. “They had read that ‘pirate sites’ used it and that they’re mining ‘cryptocurrency’.

“So, the users who didn’t know better were shocked and scared and various antivirus programs screaming in agony with false positives didn’t help either.”

According to Škvorc, the antivirus industry could also review what it sees as threats, claiming that although mining tools can be processor hungry, they are not significantly worse than many adverts that aren’t flagged. “It’s funny how they don’t flag flashy cookie ads as malware, but using CPU cycles that would otherwise be used by bad JavaScript in adverts is somehow dangerous,” he said.