Swartz killed himself just over two weeks ago as he faced trial for hacking an online collection of academic journals linked to MIT with the intent of releasing millions of research papers on to the internet.
The 26-year-old had a history of depression but family, friends and supporters said it was the threat of a prison sentence for an act he saw as a political statement that pushed him to suicide. Since his death, Swartz has become a powerful symbol for hackers and activists fighting internet controls.
The website of the commission, an independent agency of the judicial branch involved in sentencing, was replaced with a message warning that when Swartz killed himself two weeks ago "a line was crossed." In a message posted on the website and in an accompanying YouTube video, the hackers said they had infiltrated several government computer systems and copied secret information they threatened to make public.
Saying the information was like a nuclear weapon, the group said it had "enough fissile material for multiple warheads" which it would launch against the justice department and organisations linked to it.
By late Saturday morning, the USSC website was offline, but cached versions could be found where the message appeared.
Anonymous, which has been the target of numerous arrests and FBI probes, has taken a relatively high profile in several cases recently. In the small Ohio town of Steubenville, which has been rocked by rape allegations against several high school football players, the group has organised protests and posted evidence it says shows evidence of a cover-up of the alleged crimes.
Anonymous is a loosely defined collective of so-called hacktivists who oppose attempts to limit internet freedoms.
It has suffered from some high-profile arrests after attempts in recent years to attack major corporate government websites.
Swartz and Anonymous have been firm advocates of open access to information and open-source programming. At a memorial service for Swartz last weekend, several of his supporters called for those who were attempting to prosecute him to be held accountable for their actions.
Swartz had faced a possible jail sentence of 30 years, though it has since emerged he was also offered a plea deal of six months.
Officials involved in prosecuting the case have insisted they did not over-reach in their aggressive pursuit of Swartz but have faced a storm of criticism for their behaviour.
guardian.co.uk © Guardian News and Media Limited 2010
image: © Rennett Stowe
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