The hacker group Anonymous is claiming responsibility for attacks that have taken down websites run by Universal Music, the U.S. Department of Justice and the Recording Industry Association of America in retaliation for the government's removal of the Megaupload websites.

"The government takes down Megaupload? 15 minutes later Anonymous takes down government and record label sites," the Anonymous Twitter feed read.

That note was followed shortly by this one: "Megaupload was taken down w/out SOPA being law. Now imagine what will happen if it passes. The Internet as we know it will end. FIGHT BACK." The tweet referred to the Stop Online Piracy Act, an Internet piracy bill being considered in the U.S. Congress.

Megaupload.com distributed a variety of digital content, including music and movies. On Thursday, the U.S. DOJ announced that it had charged seven people who allegedly were affiliated with the site with running an organized criminal enterprise responsible for worldwide online piracy of copyrighted content. The DOJ worked with authorities in New Zealand, who arrested four of the seven people.

Megaupload.com is no longer accessible.

The action happened just a day after thousands of websites went dark in protest of bills before Congress, including SOPA, that would make it easier for authorities to force ISPs (Internet service providers) to block people in the U.S. from accessing foreign websites accused of offering pirated content. Opponents say the bills would let law enforcement shut down entire websites before the sites have been found by a court to infringe copyright.

By mid-afternoon, the people behind the Anonymous Twitter account had claimed responsibility for attacks affecting sites for the DOJ, RIAA, Universal Music, the U.S. Copyright Office, Broadcast Music Inc. and the Motion Picture Association of America. They said the FBI website was on its target list, although that site remained operational midday on the West Coast.

Nancy Gohring covers mobile phones and cloud computing for The IDG News Service. Follow Nancy on Twitter at @idgnancy. Nancy's e-mail address is Nancy_Gohring@idg.com