Japanese authorities have jailed a serial malware writer for two-and-a-half years over his latest creation.

Masato Nakatsuji, 28, was found responsible for writing a strain of malware that spread across the locally popular Winny peer-to-peer file-sharing network last summer, replacing infected files on victims' computers with the image of an orange cartoon octopus. He was convicted of property destruction charges over the creation of the so-called "ika-tako" (squid-octopus) malware. At least three confirmed victims of the malware came forward.

"It was an ingenious, planned crime to spread a computer virus over a long period of time," said presiding Judge Masaru Okabe, local English language news site the Daily Yomiuri reports. "The defendant committed the crime while he was on probation for a similar charge. I have no choice but to give him a sentence without suspension."

Nakatsuji wrote the malware while still on probation for an earlier, near identical, scam. The miscreant previously created the Pirlames (AKA Harada) Trojan, which also spread via Winny, and displayed images of anime characters while destroying music and movie files on infected PC. In the absence of any specific computer crime law in Japan at the time, Nakatsuji was found guilty in 2008 of violating copyright laws and given a two-year prison sentence, suspended for three years.

Last month Japan made the creation of computer viruses a specific criminal offence. ®