'Anonymous' threatens Justice Department

Anonymous is believed to be the loosely defined collective of so-called "hacktivists." The threat note said anger over the death of Internet activist Aaron Swartz

(CNN) -- Hackers claiming to be from the group "Anonymous" threatened early Saturday to release sensitive information pertaining to the U.S. Department of Justice.

After taking over the website of the U.S. government agency responsible for federal sentencing, the hackers posted a message signed "Anonymous," in which they demand that the United States reform its justice system or face the release of "warheads" of incriminating information.

Anonymous is believed to be the loosely defined collective of so-called "hacktivists" who oppose attempts to limit Internet freedoms.

There was a long threat note and a YouTube video and a list of files named after U.S. Supreme Court justices.

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The threat note said anger over the death of Internet activist Aaron Swartz, who committed suicide on January 11, triggered the posting.

Swartz, 26, was facing federal computer fraud charges and could have faced 35 years in prison.

His family has issued a statement saying that federal charges filed over allegations that he stole millions of online documents -- mostly scholarly papers -- from MIT through the university's computer network contributed to Swartz's decision to take his own life.

Swartz's suicide inspired a flurry of online tributes and mobilized Anonymous. They claimed credit for defacing several MIT websites in response.

A review of a cached version of the USSC.gov website shows the Anonymous message on its homepage since at least 1:40 a.m. ET.

Efforts to get to the website was unsuccessful by some by 6 a.m. E.T.