Japanese police have arrested a 17-year-old boy on suspicion of creating malware that steals private keys (passwords) that are used to access cryptocurrency wallets. He's also under investigation for using these passwords to steal funds from victims, albeit no charges have been filed.

According to an arrest warrant seen by Mainichi Shimbun reporters, the teenager hid the malware he created inside an application for viewing cryptocurrency market data in real time.

The teen then shared the trojanized app online. Police say that one of the places he shared his program was a forum for Monacoin users. Monacoin is just one of the many Bitcoin-offshoot cryptocurrencies, advertised as "the first Japanese cryptocurrency," and currently ranked 88th on CoinMarketCap based on market value.

Japanese authorities say that at least one man —a 31-year-old from Tokyo— downloaded and installed the teen's app. This man later discovered that 170 Monacoins (around $500) went missing from his wallet. He said he saw other users' warnings on the forum regarding the suspicious software, but it was too late at that point.

Police believe the number of victims is likely much higher. They are now looking to link the teenager as the person who used the wallet private keys (passwords) to steal the funds.

The teen is a third-year high school student in Kaizuka, Osaka Prefecture. He was arrested on Tuesday, January 30. He defended himself by telling police: "I didn't do it with malicious intent."