Hacking group Anonymous claimed responsibility for the shutdown of the Japanese Prime Minister’s official website. In a tweet, a hacktivist affiliated with the group asserted the “Tangodown” was a warning to stop hunting whales. Rounds of congratulations and thank-yous from online whaling critics followed.

The site was inaccessible early Thursday morning, and authorities are investigating, with no updates at this time — and possibly none to come. According to The New York Times, Japan’s Chief Cabinet Secretary Yoshihide Suga said, “We have not determined for certain that it was an attack by Anonymous, but we have received reports that they claimed responsibility.”

The attack occurred after Japan sent two whalers forth on a supposedly scientific mission to the Antarctic last week. Japan is a member of the International Whaling Commission and agreed to an international moratorium on commercial whaling thirty years ago, but continues to hunt and kill whales under the auspices of scientific research. Japanese authorities claim that the mission to the Southern Ocean is seeking information on minke whales’ reproductive habits and migratory patterns. However, it remains unclear how this information is obtained through the killing of over 300 whales, which are the essential target of this year’s hunt.

Arctic minke whales themselves are listed as “Data-deficient” on the International Union for the Conservation of Nature’s Red List, meaning there isn’t enough information about the species to determine its risk of extinction.

A United Nations Court ruled in 2014 that such “research” killed close to 1,000 whales per year, yet resulted in little scientific advancement, and Japan was banned from further Antarctic hunts. Critics assert that the 300 whales targeted this year are too many, and apparently Anonymous agrees. If research is the true aim, information can be gained without further thinning the world’s whale population.

This is not the first time Anonymous has acted to express its disapproval of whaling. Hackers gave Iceland a similar treatment in November, shutting down the websites of the Prime Minister and the ministries of the interior and the environment for about a day. Iceland is another IWC member, but also claims that its fishermen compete with whales for the fish on which its economy heavily depends. Japan’s economy is more diverse, but whaling has national cultural significance, and so clings on as a commercial enterprise.