McLEAN, Va. -- A hacker collective known as Anonymous took down several websites Thursday — including the Department of Justice — to retaliate for the federal government’s arrest of several Internet executives and the shutdown of the world’s largest file-sharing site.

Justice’s website was still down late Thursday night. The cyber-hackers also paralyzed the websites of the FBI, U.S. Copyright Office, the Motion Picture Association of America and the Recording Industry Association of America.

“The department is working to ensure the website is available while we investigate the origins of this activity, which is being treated as a malicious act until we can fully identify the root cause of the disruption,” the Justice Department commented on Twitter.

“Get some popcorn ... it’s going to be a long ... night,” reads a tweet posted Thursday night by Your AnonNews, which claims to be associated with Anonymous.

The hackers apparently took revenge after the feds shut down file-sharing site Megaupload.com earlier Thursday. Its founder and several executives were charged with violating piracy laws, federal prosecutors said.

An indictment accuses Megaupload.com of costing copyright holders more than $500 million in lost revenue from pirated films and other content. The indictment was unsealed one day after websites, including Wikipedia and Craigslist, shut down in protest of two congressional proposals intended to thwart online piracy.

The Justice Department said in a statement that Kim Dotcom, formerly known as Kim Schmitz, and three other executives were arrested Thursday in New Zealand at the request of U.S. officials. Two other defendants are at large.

MegaUpload is a “digital locker” that allows users to store files that can then be streamed or downloaded by others. Its subsidiary site MegaVideo became popular for the unauthorized downloads of movies and TV shows. Users whose uploaded content proved particularly popular were paid for their participation.

In a joint statement, the Justice Department and FBI called the action “among the largest criminal copyright cases ever brought by the United States.”

Ira Rothken, an attorney for MegaUpload, said in an interview that he only learned of the actions in a news release Thursday morning and had not yet read the entire indictment.

“Our initial impression is that the allegations are without merit and MegaUpload is going to vigorously contest them,” he said. “We have deep concerns over due process and assets being taken without the opportunity for a hearing.”

According to the indictment, the operators of MegaUpload earned more than $175 million in illegal profits and caused an estimated $500 million in harm to copyright holders.

The site is advertised as having more than 50 million daily visitors, according to federal authorities.

The indictment in the MegaUpload case was handed down by a grand jury in Virginia two weeks ago but was unsealed Thursday. It stems from a federal investigation that began two years ago.

As part of the crackdown on MegaUpload, 20 search warrants were executed in nine countries, including the United States. About $50 million in assets were also seized, as well as a number of servers and 18 domain names, the authorities said.

Four of MegaUpload’s operators have been arrested in New Zealand, while three more remain at large.