A tense territorial dispute with China has triggered cyberattacks, according to Japan-based reports.
Web sites at 19 Japanese banks and universities, among other institutions, have been hit with attacks in the wake of Japan's nationalization of the Senkaku Islands on September 11, according to Kyodo News Agency and other reports.
The Web site of the Internal Affairs and Communications Ministry statistics bureau, for example, has come under a distributed denial of service (DDoS) attack, Kyodo said.
Tohoku University, an elite science and engineering university, has also been targeted, Kyodo said.
It's not clear who's behind the attacks. So far, the Chinese government hasn't publicly addressed the reports in Japan.
The attacks were triggered on September 11 when the Japanese government purchased the Senkaku islands from private owners for about $30 million, effectively nationalizing the territory.
China disputes Japan's claim to the islands and sent Chinese navy surveillance vessels to the area last week.
And Japan's taking of the islands have sparked protests across China, according to the English-language China Daily, which wrote in an editorial dated September 20 that the "islands have belonged to China since ancient times."
And tensions were further inflamed this week on the 81st anniversary of the Manchurian Incident (also known as the Mukden Incident). In 1931, the Imperial Japanese Army bombed a Japanese railway as a pretense for invading China.