The Tokyo High Court on Friday overturned the acquittal of a man accused of secretly installing and using a cryptocurrency mining program on the computers of visitors to his website.

The court ruled that the 32-year-old website designer operated the Coinhive program without the knowledge or permission of visitors to his website. The court described the man's action as a "malicious crime used for personal gain" and fined him ¥100,000.

"Visitors were not informed of (the mining program) or given the chance to reject it," presiding Judge Tsutomu Tochigi said.

The website designer expressed dissatisfaction with the ruling. His lawyer said he would appeal.

In March last year the Yokohama District Court acquitted the man, saying the program only had a minor impact on the visitors' computers and investigators had not cautioned him against the use of the software before indicting him.

The high court, however, said such factors did not provide grounds for acquittal.

He was indicted in March 2018 on charges that he embedded Coinhive into his website between October and November of 2017. He has not been detained.

As digital currencies are not managed by governments or central banks, miners earn cryptocurrency by verifying transaction records and adding them to digital ledgers.

Coinhive starts mining on the computers of people who visit sites embedded with the program and shares the rewards between the program developer and the website operator.