A Japanese hacker who hijacked computers using malware before issuing death threats through the compromised machines has been jailed for eight years.

Yusuke Katayama, 32, threatened to blow up planes and attack a kindergarten attended by the grandchildren of Japan's Emperor Akihito before he was finally nabbed in February 2013.

The self-styled "Demon Killer" led police on a wild goose chase involving the arrest of several innocent parties throughout 2012 before he was undone by a treasure hunt that ultimately led police to a cat with a contaminated SD card in its collar.

Subsequent analysis of CCTV footage from the island of Enoshima near Tokyo showed Katayama playing with his feline "accomplice".

Katayama was previously known to the police, serving 18 months in jail for posting death threats back in 2005. The episode apparently motivated a far more serious series of crimes along the same lines, including a threat to blow up a Japan Airlines flight to New York and to run amok in the Japanese city of Osaka.

The former IT worker used the popular Japanese chat forum 2channel to infect users with the Trojan. Japanese police repeatedly arrested and detained the owners of the hacked PCs before finally catching up with Katayama.

Katayama “took full advantage of his expertise” to place violent threats online that “framed innocent people while dodging arrest himself,” according to presiding judge Katsunori Ono.

Two of these hapless suspects confessed to crimes which the National Police Agency was later obligated to admit they had had no involvement in, the Japan Times reports.

The NPA's chief has apologised and promised to improve the operations of its cyber crime division. Whether this apology placates the four people affected remains unclear.

Police held one suspect for several weeks before the media received anonymous messages referencing information that only the real culprit would have known, the BBC adds.

Bootnote

A veteran security correspondent has more on the bizarre case on Eset's blog here. This includes a link to a YouTube video of the Japanese cat being, err, collared. Subsequent examination revealed that a memory chip in the cat's collar was contaminated by malware. ®