Anonymous, the association of hacktivists, have targeted 98 websites in Japan as part of their anti-whaling campaign.
Japanese broadcaster NHK reports that the websites of government officers, aquariums, news organisations and airports have all been hacked.
The personal website of the prime minister Shinzo Abe was also attacked.
As well as animal rights defenders worldwide, Anonymous have been protesting Japan’s whaling practice since September.
Japan banned commercial whaling in 1986 but still hunts whales for scientific research.
The International Fund for Animal Welfare reports that the "Japanese whaling fleet departs twice a year and can kill up to 360 minke whales under the guise of scientific research."
Last year the International Court of Justice ruled that the Asian nation had failed to prove a scientific necessity for the annual slaughter of hundreds of wales in Antarctica and ordered the practice to cease.
Japan briefly suspended all whaling activity but after a year-long absence it resumed in spring 2015.
Meanwhile police in Japan warned that Anonymous will likely step-up attacks in the lead up to next-year’s G7 summit in Mie Prefecture.