Police departments in 10 prefectures announced June 14 that they had arrested three individuals on suspicion of illegally using computers without their owners' consent to "mine" cryptocurrency for profit, and referred 13 others to prosecutors for possible indictment in similar cases.

It is the first time for criminal charges to be pressed over illegal computer use in connection with cryptocurrency mining. The suspects include Takeo Ogino, who operates a website in Hiratsuka, Kanagawa Prefecture. The police departments involved in the investigation include those from Kanagawa, Chiba and Tochigi prefectures.

Obtaining cryptocurrencies, or digital currencies, is often likened to electronically "digging up" gold using computers. The currencies are given as a reward to contributors of computing power that is used to calculate if cryptocurrency transactions are legitimate. The more computing power one has, the faster one can receive cryptocurrencies. This apparently served as motivation to use other people's computers without consent. Exploited computers become slow and consume large amounts of electricity, as they have to do extra calculations for cryptocurrency mining.

In all cases, the 16 suspects allegedly embedded websites featuring music, sports news and other subjects with software capable of forcing viewers to participate in mining without their consent. One of the programs utilized by the suspects is called Coinhive. Released in September 2017, the program distributes 70 percent of mining profits to website owners and the rest to the developer.

Police determined that the suspects' actions were illegal because they did not indicate on their websites that viewers' computers would be used for cryptocurrency mining. Investigators allege this violates the law banning the use of computers in ways not following or against owners' intentions.

In a similar case, a website designer was ordered by the Yokohama Summary Court to pay 100,000 yen for storing a virus in March. He and his lawyer held a news conference in Tokyo on June 14 and argued that instruction of website viewers' computers is a widespread practice in online advertisements, and does not damage or negatively affect computers or steal personal information. They also said that the software does not function when the website in which it is embedded is closed, and does not direct instructions that are against the viewer's intentions or are illegal.