McLEAN, Virginia — One of the world’s most popular file-sharing sites was shut down, and its founder and several company officials were accused of facilitating millions of illegal downloads of films, music and other content.

A federal indictment Thursday accused Megaupload.com of costing copyright holders at least $500 million in lost revenue. The indictment was unsealed one day after websites including Wikipedia and Craigslist shut down in protest of two congressional proposals intended to make it easier for authorities to go after sites with pirated material, especially those with overseas headquarters and servers.

The news of the shutdown seemed to bring retaliation from hackers who claimed credit for attacking the Justice Department’s website. Federal officials confirmed it was down Thursday evening and that the disruption was being “treated as a malicious act.”

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