According to local news outlet Kahoku, a judge from the city of Amagasaki sentenced a 24-year-old man named Masato Yasuda to one year in prison but suspended the sentence for three years. This means the man will remain free, but if he breaks the law in the following three years, he'll go to prison for one year.
The man was arrested earlier this year, and according to Japanese authorities, he carried out illegal cryptocurrency mining operations on users' computers in January and February.
Authorities say the tool was downloaded over 90 times and helped Yasuda make 5,000 yen worth of Monero cryptocurrency, which is around $45.
"The defendant regretted what he did, learning information ethics and other matters," said the judge presiding over the case, as quoted by Japanese news outlet The Mainichi.
The use of the library is contentious, especially if site owners don't request permission from users, and the library has become a favorite among malware authors who often deploy it on hacked sites.
While Yasuda didn't use the library on a site, he is the first ever person to be sentenced for using it.
Other sentences are most likely to follow because last month, Japanese authorities from 10 prefectures arrested 16 individuals suspected of involvement in cryptojacking, a term used to describe the practice of secretly adding Coinhive to a site.
Officials believe the 16 suspects hacked sites and inserted the Coinhive library into their code. The most money earned among the 16 suspects was the equivalent of about 120,000 yen ($1,100).
Yasuda's lawyer is also representing a software engineer named Moro in court, who says he was questioned by police, who then searched his house, seized his laptop and fined him 100,000 yen ($905) for using Coinhive on his personal site as part of a short test between late September and early November last year.