That's the cyber news from Mashable.com. From the site's report---which elsewhere says the attack was intended as retaliation for the prosecution of Aaron Swartz:
The hacktivist group Anonymous hacked the US federal sentencing website early Saturday, using the page to make a brazen and boisterous declaration of "war" on the U.S. government.
The group claims mysterious code-based "warheads", named for each of the Supreme Court Justices, are about to be deployed.
As of midnight Pacific time, the front page of Ussc.gov — the Federal agency that establishes sentencing policies and practices for the Federal courts — is filled with a long screed in green on black, together with this YouTube video:
UPDATE (12:45 p.m.): according to this account, from Zdnet, the U.S.S.C.'s website is down, and has since been dropped from the Domain Name System. Additionally, according to the Zdnet report:
It appears that via the U.S. government website, Anonymous had distributed encrypted government files and left a statement on the website that de-encryption keys would be publicly released (thus releasing the as-yet unkonwn information held on the stolen files) if the U.S. government did not comply with Anonymous' ultimatum demands for legal reform.
The FBI is investigating the attack, according to Richard McFeely, of the bureau's Criminal, Cyber, Response, and Services Branch. "We were aware as soon as it happened and are handling it as a criminal investigation," McFeely said in an emailed statement. "We are always concerned when someone illegally accesses another person's or government agency's network."