Photo/IllutrationThe Asahi Shimbun

Police from 10 prefectures have nabbed 16 individuals suspected of installing programs into the computers of unsuspecting users to mine for cryptocurrency.

Three men were arrested on suspicion of illegal use of what were defined as computer viruses, while 13 other men had their papers sent to prosecutors for the same suspicion.

The case against the 16 men aged between 18 and 48 was announced on June 14, although the first arrests were made in March.

The suspects all operated their own websites, and they allegedly sent programs to the computers of site users without their consent.

The programs kicked into action on the users’ computers to conduct the often tedious and time-consuming task of mining to earn cryptocurrency.

One program used was Coinhive, which mines for the Monero cryptocurrency.

Coinhive can be obtained over the Internet, but one of the suspects made a program very similar to Coinhive and sent it to users’ computers.

For that reason, the man was also arrested on suspicion of creating a computer virus.

Cryptocurrency earned through mining using the Coinhive program is shared, with 70 percent going to the website operator and the remainder kept by Coinhive.

The most money earned among the 16 suspects was the equivalent of about 120,000 yen ($1,100).

Police have monitored the Coinhive program since its release in September 2017 to determine where it was being installed.

Police decided to arrest the men because they determined legal violations were made when the site users were not asked for their consent. In addition, the users’ computers consumed more electricity after the mining program was activated.

The Coinhive program had been criticized from the very start because it could be installed without the knowledge of the computer user. Major computer anti-virus makers have taken measures to block the installation of the Coinhive program, which was considered a virus by those software companies.

Hisashi Sonoda, a professor at Konan Law School who is knowledgeable about cybercrimes, said the arrests were likely made because consent of the site users was not obtained.

At the same time, he said the sudden arrests may have been somewhat excessive because there are no legal precedents on how to handle the use of such programs.