New, strict Japanese copyright law that could imprison people for illegally downloading copyrighted content incited the attack.
A website, dubbed AnonPR, claimed to speak for the group and launched Operation Japan on June 25. From the site:
Japan, home to some of the greatest technological innovations throughout history has now decided to go down the path as well and cave into the pressures of the content industry to combat piracy and copyright infringement. Earlier this week Japan approved an amendment to its copyright law, which will give authorities the right to imprison citizens for up to two years simply for downloading copyrighted material
We at Anonymous believe strongly that this will result in scores of unnecessary prison sentences to numerous innocent citizens while doing little to solve the underlying problem of legitimate copyright infringement.
"We are aware of the Anonymous statement referring to the new copyright law, but we don't know at this point if the cyber-attacks are linked to the group," said official Takanari Horino at the Finance Ministry.
One of Anonymous' strengths is that it is anonymous. This is also why some Japanese bureaucrats might be scratching their heads, wondering if they were attacked by the real Anonymous or simply by anonymous people.
Website attacks prompt probe [Japan Times]