Hacking shut down the Department of Justice's website Thursday, and several other organizations that support anti-piracy efforts.

The victims were: Universal Music Group, the Motion Picture Association of America (MPAA), the Recording Industry Association of America (RIAA) and the U.S. Copyright Office.

YourAnonNews, a Twitter account affiliated with the group, said this was its biggest attack yet.

The immediate impetus for the attack was the Department of Justice's .The DOJ also shut down the site.

Wednesday, thousands of sites shut down and several prominent legislators withdraw their supports of the respective bills.

Each of Anonymous' victims has been a fervent advocate of anti-piracy legislation, especially MPAA President Christopher Dodd who has sharply criticized those websites that went black.