The state Security Operation Center is investigating a distributed denial of service attack on Sunday that targeted the state’s official government website and a site maintained by the Thirty Meter Telescope project.

A group calling itself Operation Green Rights, which purports to be affiliated with the activist hacker group Anonymous, announced the attack via social media and its own blog around 10 a.m. Hawaii time.

“TMT today was the victim of an unscrupulous denial of service attack, apparently launched by Anonymous, which caused the TMT website server to be unavailable for approximately two hours,” said TMT Hawaii community affairs manager Sandra Dawson in a statement released Sunday evening. “The incident is being investigated.”

The state site was already back online when officials learned of the attack around 4:30 p.m.

Cindy McMillan, communications director for Gov. David Ige, said she could not confirm that the site was actually down.

The Operation Green Rights posted screen shots “Unable to Connect” and “Site Offline” messages from the two targeted sites along with the heading “Anonymous with the Hawaiian natives against #TMT” and a short message: “Nothing will ever justify the destruction of ecosystems; filthy money can never replace them. Stand with the Hawaiian natives against #TMT (Thirty Meter Telescope).”

The group’s Twitter posting drew relatively minimal reaction, with 18 retweets and 33 “favorites.”

Denial of service attacks typically bombard a server with multiple external communications requests so that the server must reset or so that the server is rendered incapable of communicating normally with its intended users.