The malware, which has been distributed via the P2P file-sharing network Winny, was a Trojan horse designed to delete music and movie files. While doing that, the malware would display of popular anime characters.

The Trojan horse, which earned the name Harada in the Japanese media, is believed to be related to the Pirlames Trojan horse discovered by net security firm Sophos in Japan last year.

"Normally you would expect malware writers to be arrested for breaking into computers with their code or damaging data, but in this case he is accused of breaching copyright because he used cartoon graphics without permission in his Trojan horse. Because this is the first arrest in Japan of a virus writer it’s likely to generate a lot of attention and there will be many people watching to see the outcome," said Graham Cluley, senior technology consultant for Sophos.

The three men arrested by the police are 24-year-old student Masato Nakatsuji, who is said to be the author of the Trojan, and Shoji Sakai (39) and Katsuhisha Ikema (35), a duo responsible with distributing the malware.