After turning himself in to authorities yesterday morning, Swartz made an initial appearance in US District Court. He posted a $100,000 unsecured bond, cosigned by his parents, who were at the hearing.

In one case in October 2010, he allegedly used two computers, and the download pace “was so fast that it brought down some of JSTOR’s computer servers,’’ the court records stated. As a result, users had difficulty getting access to the system, prosecutors said, and at one point licensed access for them was cut off.

Swartz already had regular, licensed access to the database through his work at Harvard. But prosecutors said he was so committed to the immediate acquisition of materials that he used special software to enable the quick downloading. He changed the Internet protocol address on his computer several times to circumvent security guards, according to court records.

By yesterday afternoon, however, Swartz had received an outpouring of support from colleagues and friends who took to blogs and websites to defend his work and maintain that the charges against him are heavy-handed. More than 15,000 people had signed a letter of support for Swartz on the website DemandProgress.org .

“Stealing is stealing, whether you use a computer command or a crowbar and whether you take documents, data, or dollars,’’ US Attorney Carmen M. Ortiz said in a statement. “It is equally harmful to the victim, whether you sell what you have stolen or give it away.’’

Of the 4.8 million documents downloaded, 1.7 million should only have been available for purchase through a sales service.

Prosecutors say Swartz violated JSTOR’s licensing agreement prohibiting mass downloading of documents and the use of those documents for anything other than personal work. Authorities said Swartz planned to distribute the information free on file-sharing websites, cheating the archive of subscription fees, some as high as $50,000.

According to the indictment, Swartz hacked into the MIT network so he could mass download millions of documents from an archive operated by the nonprofit group JSTOR. When computer security tried to block his access, he allegedly broke into a basement closet of an MIT building to hard-wire his computer to the network.

Swartz, 24, who at the time of the alleged hacking in fall 2010 was a fellow at Harvard University’s Edmond J. Safra Center for Ethics, was charged in an indictment unsealed yesterday with wire fraud, computer fraud, unlawfully obtaining information from a protected computer, and recklessly damaging a protected computer. He faces up to 35 years in prison and a $1 million fine.

Aaron Swartz, a Cambridge web entrepreneur and political activist who has lobbied for the free flow of information on the Internet, was charged in federal court with hacking into a subscription-based archive system at MIT and stealing more than 4 million articles, including scientific and academic journals.

Asked about Swatz yesterday, a Harvard spokesman would only say that Swartz had a 10-month fellowship and that he was placed on leave once university officials became aware of the federal investigation. His fellowship ended last month.

In 2008, Swartz was investigated in a similar case in the downloading of millions of documents from the federal court system during a trial run of a federal database. No charges were brought.

Supporters and colleagues of Swartz defended him yesterday, saying he has worked for the free, open access of information and data. Four years ago, he led the development of the group Open Library, a project to collect information about every book published. At age 14, Swartz helped develop RSS, a system for quickly distributing updated Web pages to other Internet sites or to people who wish to receive them.

David Segal - executive director of Demand Progress, a nonprofit political action group that Swartz founded - said yesterday that the charges amount to “trying to put someone in jail for allegedly checking too many books out of the library.’’

James Jacobs, government documents librarian at Stanford University, met Swartz when he was a student there and also denounced the arrest.

“From what I know about Aaron, he is interested in researching about networks and information, and so I gather that what he was doing was for research,’’ Jacobs said. “I don’t think that he was stealing anything. I don’t think Aaron is capable of doing that kind of thing.’’

Segal said in a statement that the alleged victims in the case, MIT and JSTOR, have settled their claims against Swartz and asked the government not to prosecute.

But Heidi McGregor, vice president of communications for JSTOR, said her agency never told the government not to prosecute Swartz.

She said her company’s focus was on “making sure the data was secure and the data was not disseminated, so we were happy we got that result.’’ McGregor said she could not comment on the federal government’s decision to bring charges.

MIT officials did not respond to a request for comment.

Jerry Cohen - an attorney with Burns & Levinson of Boston who specializes in copyright, licensing, and publication law - said yesterday that the allegations against Swartz are serious.

Even nonprofit groups such as JSTOR have the right to set up commercial arrangements to distribute copyrighted material, he said. “They can’t leave themselves open to someone who wants to take it. What he has done can be disruptive of that system.’’

Cohen added, however, that past cases have been resolved in the civil court system, with the goal being the halting of the inappropriate work.

Cohen said the use of criminal charges here is the latest in what has been a government trend to prosecute such cases, which he described as taking “a sledgehammer to drive a thumb tack.’’

“It might be taking too big a weapon,’’ he said. “It’s intended to terrorize the person who’s indicted and others who might be thinking of the same thing.’’

Hiawatha Bray of the Globe staff contributed to this report. Milton J. Valencia can be reached at valencia@globe.com. Follow him on Twitter @MiltonValencia.

© Copyright 2011 Globe Newspaper Company.