Computer prodigy Aaron Swartz, who co-developed Reddit and RSS before becoming a digital activist, has died aged 26.

Ellen Borakove, a spokeswoman for New York's chief medical examiner, said he was pronounced dead late on Friday (local time) in the city's Brooklyn borough.

She said Swartz had committed suicide.

Swartz helped develop the RSS tool for users to get updates from blogs, news headlines and other online content.

He helped develop Creative Commons laws and co-founded the social news website Reddit, but left the company after it was acquired by Wired magazine owner Conde Nast.

He was about to stand trial on federal criminal charges in a controversial fraud case.

"Information is power. But like all power, there are those who want to keep it for themselves," he wrote in an online post in 2008.

"The world's entire scientific and cultural heritage, published over centuries in books and journals, is increasingly being digitised and locked up by a handful of private corporations... sharing isn't immoral - it's a moral imperative.

"Only those blinded by greed would refuse to let a friend make a copy."

That belief - that information should be shared and available for the good of society - prompted Swartz to direct Demand Progress, a political action group that campaigns against internet censorship.

The group led a successful campaign to block a bill introduced in 2011 in the US House of Representatives called the Stop Online Piracy Act.

The bill, which was withdrawn amid public pressure, would have allowed court orders to curb access to certain websites deemed to be engaging in illegal sharing of intellectual property.

Swartz and other activists objected on the grounds it would give the government too many broad powers to censor and squelch legitimate web communication.

But Swartz faced trouble in July 2011, when he was indicted by a federal grand jury of wire fraud, computer fraud and other charges related to allegedly stealing millions of academic articles and journals from a digital archive at the Massachusetts Institute of Technology.

He was released on bond, and his trial was scheduled to start later this year.

Swartz, who pleaded not guilty to all counts, faced 35 years in prison and a $1 million fine if convicted.

'Prodigious skills'

Online tributes to Swartz flooded across cyberspace as news of his death spread.

In a statement posted online, Swartz's family remembered him as a man who had made the world a brighter place.

"Aaron's commitment to social justice was profound, and defined his life," the statement said.

"He was instrumental to the defeat of an internet censorship bill; he fought for a more democratic, open, and accountable political system; and he helped to create, build, and preserve a dizzying range of scholarly projects that extended the scope and accessibility of human knowledge.

"He used his prodigious skills as a programmer and technologist not to enrich himself but to make the internet and the world a fairer, better place.

"His deeply humane writing touched minds and hearts across generations and continents. He earned the friendship of thousands and the respect and support of millions more."

Tim Berners-Lee, who is credited as the most important figure in the creation of the World Wide Web, commemorated Swartz in a Twitter post on Saturday.

"Aaron dead," he wrote.

"World wanderers, we have lost a wise elder. Hackers for right, we are one down. Parents all, we have lost a child. Let us weep."

Fellow technology activist Cory Doctorow met Swartz at age 14 or 15.

"In so many ways, he was an adult, even then, with a kind of intense, fast intellect that really made me feel like he was part and parcel of the internet society," Doctorow wrote on the Boing Boing blog.

"But Aaron was also a person who'd had problems with depression. Whatever problems Aaron was facing, they will go unsolved forever."

Doctorow later wrote a blog claiming that the trial had contributed to Schwartz's death.

Following the activist's 2011 arrest, his anti-censorship group Demand Progress said the prosecution did not make sense.

"It's like trying to put someone in jail for allegedly checking too many books out of the library," the group's executive director David Segar said in a statement at the time.

Harvard Law School's Safra Centre for Ethics director Lawrence Lessig said there is "no way to express the sadness of this day".

"To the co-creator of RSS, of the Creative Commons architecture, of part of Reddit and of endless love and inspiration and friendships, rest," he added in an online post.

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ABC/AFP/Reuters