Under Japanese law writing malicious code isn't illegal, according to antivirus vendor Sophos. Japanese authorities are therefore prosecuting the alleged writer of a particular piece of code, and two others, as the code was allegedly distributed using unauthorised anime images.
From the Sophos press release:
"It isn't illegal to write viruses in Japan, so the [alleged] author of the Trojan horse has been arrested for breaching copyright because he used cartoon graphics without permission in his malware. Because this is the first arrest in Japan of [an alleged] virus writer it's likely to generate a lot of attention and there may be calls for cybercrime laws to be made tighter," said Graham Cluley, senior technology consultant for Sophos.