The Japanese Government is facing more problems from computer hackers, just a day after an emergency meeting decided to set up a task force to prevent any further incidents.

Police have launched an investigation after hackers tampered with two more government websites.

In one instance, they invaded the homepage of the Economic Planning Agency's National Institute for Research Advancement, substituting the welcome message with "Nippon is rotten animal" repeated six times.

Nippon is the Japanese word for Japan.

The intruders also directed visitors to the Web site of Playboy magazine.

There have been at least four hacker attacks on government websites this week.

Two have accused Japan of denying the Rape of Nanking, the Japanese army's massacre of civilians during Tokyo's 1937-38 occupation of the Chinese city now known as Nanjing.

In one case, the hackers erased important data from the Management and Co-ordination Agency's website, including the population census.

It was thought to be the first hacking of the country's government computer system.

Computer security

The hackers broke into the sites just days after officials decided to bring Japan up to US standards of computer security by 2003 and to draw up a plan to fight hackers by the end of this year.

These measures will now be enacted within two years, the Nihon Keizai newspaper said.

Cabinet ministers met police on Wednesday to discuss ways to combat the cyber-terrorism.

Tokyo is also understood to be asking the United States for assistance.

Wartime past

The message referring to the Nanking massacre said: "The Chinese people must speak up to protest the Japanese government for refusing to acknowledge the historical misdeed of the 1937 Nanking Massacre".

The message was signed off: "Brazil p00 hackerz".

Hundreds of thousands of civilians were massacred by Japanese troops during the 1937-38 occupation of the central Chinese city.

Last week, a group of extreme right wing Japanese held a conference in Osaka to deny the massacre.

The Chinese Government lodged protests about the gathering. But the Japanese Government, which acknowledges that the incident was no fabrication, failed to ban the meeting.