A Japanese man was sentenced to eight years in jail last week after being found guilty of remotely hacking computers and using them to send death threats and other malicious messages online.

Former IT engineer Yusuke Katayama, 32, was sent down by Tokyo District Court after the high profile case in 2012 in which he used popular Japanese internet forum 2channel to infect users with a “remote control virus” dubbed “iesys.exe.”

He is then alleged to have used these victim machines to post the messages, which included a bomb threat to a New York-bound Japan Airlines plane, forcing the carrier to turn back to Narita Airport, according to the Japan Times.

Katayama is also said to have sent a bomb threat to a kindergarten attended by the Emperor’s grandchildren and a warning of an impending killing spree on the streets of Osaka.

Police were widely criticized during the case after wrongfully arresting four people in Tokyo, Osaka, Fukuoka and Mie prefectures.

Two of them were apparently forced into making false confessions, despite being unaware that their computers were being remotely controlled by Katayama, who called himself the ‘Demon Killer’ online.

Only when another message was sent while some of the victims were still in custody did the police finally realize their mistake.

It has called into question the ability of the National Police Agency to respond to cybercrime.

Katayama was finally arrested in February 2013 after constructing an elaborate treasure hunt via several cryptic emails sent to media outlets on New Year’s Day.

They eventually led police to a cat, which they found on a small island near Tokyo with an SD card attached to its collar bearing the malware.

After studying CCTV footage from the island of Enoshima, police apparently spotted Katayama playing with the feline.

Katayama had pleaded not guilty until May last year, when he changed his plea after being caught trying to destroy incriminating evidence.

“[His] deeds, in a way, are a form of pleasure-seeking crime, one that’s symptomatic of this internet age, where people somehow frustrated with their lives no longer stab or punch somebody directly to vent their anger,” his lawyer Hiroshi Sato said, according to the report.

“They instead turn to the world of cyberspace, where they deceive strangers and take grim satisfaction in watching them suffer.”