Former U.S. intelligence contractor Edward Snowden denied Thursday that he had ever stolen his co-workers’ passwords or otherwise tricked them to gain access to thousands of classified documents that he leaked to news organizations.

In an extensive online question-and-answer session, Snowden also indicated that he would like to return to the United States, but made clear that he would do so only if he were protected from prosecution.

“Returning to the US, I think, is the best resolution for the government, the public, and myself, but it’s unfortunately not possible in the face of current whistleblower protection laws,” he wrote in an exchange recorded on a Web site run by his supporters.

The session marked the first time that Snowden has fielded questions submitted by the public on subjects including his rationale for stealing a trove of classified documents from the National Security Agency, and his views on the intense debate triggered by the exposure of far-reaching surveillance programs described in those secret files.

Snowden’s online appearance came just days after President Obama delivered a speech announcing that he will seek to end the NSA’s role in collecting Americans’ phone records. On Thursday, an independent privacy board said the program is illegal and should be shut down.

Snowden, who has been granted temporary asylum in Russia, has become increasingly outspoken in recent months — emboldened by developments that have raised questions about the legality of the NSA program, but also apparently determined to defend his motivations and behavior.

“I never stole any passwords, nor did I trick an army of co-workers,” Snowden wrote, addressing allegations that he had exploited his colleagues’ computer accounts to gain access to the files he took. He did not provide new details on how he obtained the documents. He was working as an information technology contractor at an NSA facility in Hawaii last year when he fled first to Hong Kong and then to Moscow.

U.S. officials have described the theft as one of the most extensive and damaging security breaches in the nation’s history, undermining programs designed to help protect the country from terrorist plots.

In his speech last week, Obama referred to Snowden by name, saying that his disclosures had “often shed more heat than light, while revealing methods to our adversaries that could impact our operations in ways that we may not fully understand for years to come.”

But Snowden cast his actions in more noble terms, saying that he became increasingly dismayed by the scope of surveillance programs that, in his view, violated the Constitution and threatened basic principles of privacy in the United States and abroad.

Governments “are seizing billions and billions and billions of innocents’ communication every single day,” Snowden said, “not because it’s necessary . . . but because new technologies make it easy and cheap.”

Snowden’s disclosures exposed not only the NSA program that has gathered phone records of Americans, but others that have been used to intercept billions of e-mails and other communication records overseas, and to monitor the cellphones of world leaders, including German Chancellor Angela Merkel.

Attorney General Eric H. Holder Jr. on Thursday became the latest senior Obama administration official to dismiss the idea of granting Snowden immunity from prosecution to coax him into returning to the United States, which would enable U.S. officials to question him and learn more about the extent of the material he took.

“If Mr. Snowden wanted to come back to the United States and enter a plea, we would engage with his lawyers,” Holder said during an appearance at the University of Virginia. “The notion of clemency isn’t something that we were willing to consider.”

Snowden argued that he should be shielded from prosecution by whistleblower laws designed to protect government employees who report fraud or abuse from retaliation, noting that contractors are not covered under those measures.

“I still made tremendous efforts to report these programs to co-workers, supervisors, and anyone with the proper clearance who would listen,” Snowden said. “The reactions of those I told about the scale of the constitutional violations ranged from deeply concerned to appalled, but no one was willing to risk their jobs, families, and possibly even freedom.”

The questions for Snowden were submitted by users of the Twitter social networking site. His responses showed a keen awareness of even the latest developments in the surveillance debate in Washington.

He quoted from a report by the administration’s Privacy and Civil Liberties Oversight Board just hours after its official release, and called particular attention to its conclusion that there was no evidence that the government’s collection of U.S. phone records had allowed it to uncover “even a single plot.”