WASHINGTON - Hackers on Saturday took down a US Justice Department website, in what was believed to be retribution for the death of an internet activist.

The website of United States Sentencing Commission, the agency responsible for federal sentencing guidelines, was taken down. Hackers also posted a message demanding the United States reform its justice system or they would leak sensitive information obtained in the attack.

According to numerous news reports, the infamous hacker group "Anonymous" was suspected to be behind the attack. Reports quoted a letter from the group saying it hijacked the website to avenge the death of Aaron Swartz, an internet activist who committed suicide earlier this month.

Reports indicated federal prosecutors had aggressively pursued Swartz for allegedly downloading millions of academic articles with the intention of distributing them for free, before he committed suicide on January 11. He was facing federal computer fraud charges and could have served 35 years in prison if convicted.

Richard McFeely, executive assistant director of the FBI's Criminal, Cyber, Response, and Services Branch, was quoted as saying the bureau was immediately aware of the threat and is " handling it as a criminal investigation."

The US Sentencing Commission also issued a statement saying its website was in the process of being restored Saturday.