On Thursday, the U.S. Justice Department closed down Megaupload, a popular file-sharing site, and its executives were indicted by the Justice Department in what the authorities said was “among the largest criminal copyright cases ever brought by the United States,” Wired Threat Level reports.

In response, the Department of Justice, FBI, and some entertainment sites were shut down in what Wired calls “the biggest denial-of-service attacks in Internet history.” Most were back online Friday morning, CNN reports.

“Hacktivist” collective Anonymous took credit for taking down the sites, says CNN. Anonymous said ten websites were targeted. It posted a YouTube video, “Don’t Mess With Us,” saying the action heralded the beginning of “a new era.”