Supporters claim 'digital Robin Hood' has done no more than 'checking too many books out of the library'

A self-styled digital Robin Hood downloaded more than 4 million academic articles before being tracked down by US authorities in a case that promises to become a cause célèbre for data use and freedom of information.

A grand jury in Massachusetts has indicted Aaron Swartz, a 24-year-old programmer and fellow at Harvard University's Safra Centre for Ethics, on charges of wire and computer fraud for his marathon downloading spree.

The indictment also alleges that Swartz caused damage of at least $5,000 (£3,000) to computers and unlawfully obtained information over more than three months while he was copying the huge cache of articles from the database of Jstor, the giant US-based online academic repository.

Starting with a standard Acer laptop, Swartz began by using anonymous log-ins on the network of the Massachusetts Institute of Technology (MIT) in September 2010. As the size of his downloads began to alarm MIT and Jstor staff they kept trying to block Swartz's access – only for the 24-year-old to evade their attempts using simple techniques to disguise his log ins and mask his computer.

In desperation, Jstor eventually blocked the entire MIT network from access to its vast database for several days in October 2010 – cutting off one of the world's premier research universities from the millions of scientific journals and academic articles Jstor holds.

But even then, the talented coder is alleged to have bypassed them completely by entering a restricted network interface room on MIT's campus and wiring his equipment directly to its network.

According to the indictment, at one point Swartz's downloads were bringing down some of Jstor's servers: "This was more than 100 times the number of downloads during the same period by all the legitimate MIT Jstor users combined.

If convicted Swartz faces maximum jail terms of 35 years and possible fines of up to $1m. Swartz appeared in court on Wednesday and was released on bail of $100,000.

Harvard University said it had placed Swartz on leave for the remainder of his fellowship.

Swartz is a well-known digital activist, the founder of online group Demand Progress and for being a brilliant programmer. His arrest set off a war of metaphors between the federal authorities and his supporters over what it is exactly that Swartz planned to do with the trove of 4.8m articles.

The indictment filed in the US district court in Massachusetts said: "Swartz intended to distribute a significant portion of Jstor's archive of digitised journal articles through one of more filesharing sites."

US attorney Carmen Ortiz said: "Stealing is stealing, whether you use a computer command or a crowbar, and whether you take documents, data or dollars. It is equally harmful to the victim whether you sell what you have stolen or give it away."

Swartz's defenders correctly reply that copying files – especially from publicly available research databases – cannot be equated with stealing.

"It's like trying to put someone in jail for allegedly checking too many books out of the library," said David Segal, the executive director of Demand Progress, in a statement after Swartz was charged.

According to Demand Progress, MIT has already reached a settlement with Swartz, while Jstor said: "We secured from Mr Swartz the content that was taken, and received confirmation that the content was not and would not be used, copied, transferred, or distributed."

That has left some observers puzzled as to why the federal prosecutors have gone ahead with the case, especially as Jstor – the most obvious victim in the affair – publicly announced: "Our interest was in securing the content. Once this was achieved, we had no interest in this becoming an ongoing legal matter."

The other mystery is what Swartz may have been planning to do with the huge cache of PDF documents.

In 2009, Swartz attracted the attention of the FBI after he legally downloaded about 20m pages of court documents from the federal judiciary and distributed them free across the internet.

Demand Progress launched an online petition backing Swartz and received more than 40,000 messages of support.