The US Federal Communications Commission (FCC) website was deliberately attacked on 8 May, the regulator has said.
The incident began hours after comedian John Oliver criticised FCC plans to reverse US net neutrality rules.
Mr Oliver urged people to post to the site’s online commenting system, protesting against the proposals.
The FCC said that issues with the site were caused by orchestrated attacks, not high volumes of traffic.
“These actors were not attempting to file comments themselves; rather they made it difficult for legitimate commenters to access and file with the FCC,” chief information officer Dr David Bray said in an official statement.
“While the comment system remained up and running the entire time, these distributed denial of service (DDoS) events tied up the servers and prevented them from responding to people attempting to submit comments.”
‘Trolling the trolls’
In his Sunday night show Last Week Tonight, Mr Oliver called on viewers to visit a website that would direct them to the correct page on the FCC site to leave their comments.
“Every internet group needs to come together… gamers, YouTube celebrities, Instagram models, Tom from MySpace if you’re still alive. We need all of you,” he said.
His plea came after FCC chairman Ajit Pai said in April that he would review rules made in 2015 that require broadband companies to treat all online traffic equally.