Messages on those forums last week had called for cyber attacks on the 80th anniversary of the Sept. 18, 1931 "Mukden Incident," when the Japanese military staged an attack against a railroad in the Manchurian region of northern China. The incident was used as a pretext by Japan to invade and occupy Manchuria.

The NPA said that several Japanese government sites were targeted last week, and that the attacks made them difficult to access at times.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at , on or subscribe to . His e-mail address is .

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in Computerworld's Cybercrime and Hacking Topic Center.