The websites of at least 19 Japanese banks, universities and other institutions have come under cyber-attack since Japan nationalized the Senkaku Islands on Sept. 11 despite objections from China and Taiwan, the National Police Agency said Wednesday.
The electronic attacks made accessing the sites temporarily impossible. Some of the attackers also altered content on the sites, the NPA said.
An NPA official said the attacks appear to be originating in China, judging by the fact that more than half of the sites were singled out for attack on the bulletin boards of Chinese hacking groups or in major chat sites.
The Tokyo Institute of Technology said the website of its Center for the Study of World Civilization was hacked to expose personal data on 1,068 people who had taken part in events at the center. The data included names and telephone numbers.
Although the university could not verify the website attack was linked to the protests that have broken out over the disputed islands in the East China Sea, it said the main page was covered with images of the Chinese flag. The university shut down the site.
Meanwhile, Internal Affairs and Communications Minister Tatsuo Kawabata said the site of the Statistics Bureau had been targeted by a combined 7½ hours of intermittent attacks since Saturday.
The attacks appeared to be "distributed denial of service" attacks, in which a website's server is flooded with so many access requests over a short span of time that access becomes impossible, the ministry said.
On Sunday afternoon, when the attacks were most intense, 95 percent of traffic to the bureau's website was coming from China, Kawabata said. The website returned to normal Wednesday morning and its contents have not been tampered with since, the ministry said.
The targets included the Defense Ministry, a site for courts run by the Supreme Court and Tohoku University Hospital, which saw its homepage defaced by the addition of a Chinese flag.
A raft of posts on a major Chinese chat site meanwhile said, "Don't invade Diaoyu," and called for cyber-attacks on Japan. The posts peaked on Tuesday, the 81st anniversary of the Manchurian Incident, in which the Imperial Japanese Army bombed a Japanese railway as a pretense for invading China, the agency said. The incident is also known as the Mukden Incident.
Police and other authorities are investigating the attacks on suspicion of obstruction of business and illegal computer access. They have strengthened their monitoring of Chinese Web sites and urged the Japanese entities targeted by the Chinese hacker group to take precautions against further attacks.