A night view of Tokyo where police is investigating a hacking case (wikiCommons) Reuters

Following the directions of a mysterious hacker, Japanese police have found a memory card believed to contain the code to a computer virus hidden in a cat's collar, .

Detectives seized the feline on an island near Tokyo following instructions e-mailed to Japanese media by the hacker, who claims to be responsible for a series of recent online threats.

The cat-hunt was part of the hacker's challenge to Japanese police which he/she described as his "new game", AFP reported.

Earlier in 2012, various threats of terrorism and mass murders across Japan were posted online by anonymous users.

A thereat to kill people indiscriminately in Osaka was posted on the municipal government website in July, followed by other grim warnings.

Posters also claimed that a terrorist attack was going to strike the Tokyo kindergarten attended by Emperor Akihito's grandchildren, and a holy shrine was going to be blown up in the Mia province.

None of the threatened events became reality, but each prompted an unnecessary alert and deployment of police forces.

In October, Japan's National Police Agency (NPA) arrested four individuals, saying the false threats had been sent from their personal computers.

However, after a few days, NPA had to publicly apologise and free the four men, as the mysterious hacker claimed he was in fact behind the messages.

In an email sent to a Tokyo lawyer, the hacker claimed he had sent the threats after infiltrating the four arrested men's PCs.

The hacker corroborated his claim with information that police admitted only the crime's perpetrator could have known.

"You cannot dismiss such attacks as one by hackers simply out to cause mischief for their own pleasure. Many people could be misidentified as attackers without their knowledge," Itsuro Nishimoto, a senior executive at an Internet security company in Tokyo, told the Asahi Shimbum.

In December, NPA put an unprecedented ¥3m (£21,000) bounty on the hacker's head. Then, on New Year's Day, several media received a new message from the hacker.

"This is an invitation to a new game," the email read, according to the Sankei Shimbun daily.

It contained a series of riddles that, once solved, was supposed to reveal the location of a memory card containing the code to the "iesys.exe" virus or "Remote Control Virus" the hacker used to infiltrate computers without being tracked.

The riddles led police to unsuccessfully search a mountain in Tokyo, before a later e-mail said the memory stick was in fact attached to a cat's collar.

Cat Collar Japan
Japanese Police found a memory card in a cat's collar near Tokyo following a Hacker's directions (WikiCommons)