Following yesterday’s shutdown of the file hosting site MegaUpload by the United States Department of Justice, hacking group Anonymous have retaliated by bringing down the DOJ’s website overnight, as well as those of the FBI, the Record Industry Association of America, the Motion Picture Association of America and Universal Music.

The attack, dubbed “Operation Payback” began as a retaliation to the DDoS directed at MegaUpload that brought down the torrent site and the arrests of its founders. Anonymous has put together a manifesto of sorts for Operation Payback which can be found on Wikipedia.

A DOJ spokeswoman told CNNMoney “We are having website problems, but we’re not sure what it’s from.” The answer was revealed by Anonymous on Twitter, with the tweet “justice.gov & universalmusic.com TANGO DOWN! You should have EXPECT US! #Megaupload” explaining why the sites were down.

Barrett Brown, unofficial spokesman for Anonymous, told RT.com that “more is coming”, and that the hacking group with “damage campaign raising abilities of remaining Democrats who support SOPA.”

This comes during a week that has seen a lot of focus on the Stop Online Piracy Act, which if passed by US Congress would shut down file sharing sites such as MegaUpload. On Wednesday there was the Wikipedia blackout, supported by other sites in an act of protest about the free exchange of information over the internet.