The Guardian via AP, file Edward Snowden

Edward Snowden, the former National Security Agency contractor whose leaks revealed previously classified information about the extent of U.S. surveillance practices, made an argument for the end of mass data collection Thursday — but said not all spying is bad.

The comments emerged from a live chat held on the freesnowden.is website Thursday.

Questions were submitted on Twitter using the #AskSnowden hashtag. The website hosting the Q&A wrote Snowden was "expected to give his first reaction" to President Barack Obama's national security speech last week, in which the president announced a series of proposals that would reduce some of the latitude given to the NSA in the name of homeland security.

In reply to a question regarding the timing of Obama's speech last week, Snowden yet again attacked the NSA's mass collection practices, indicating they are illegal and should be ended.

"When even the federal government says the NSA violated the constitution at least 120 million times under a single program, but failed to discover even a single 'plot,' it’s time to end 'bulk collection,' which is a euphemism for mass surveillance," he wrote. "There is simply no justification for continuing an unconstitutional policy with a 0% success rate."

However, Snowden explained that while he takes issue with "indiscriminate mass surveillance," not all intelligence collection practices are bad.

"Not all spying is bad," Snowden wrote, adding: "The NSA and the rest of the U.S. Intelligence Community is exceptionally well positioned to meet our intelligence requirements through targeted surveillance — the same way we’ve always done it — without resorting to the mass surveillance of entire populations."

In reply to a different question, Snowden emphasized his argument: "Collecting phone and email records for every American is a waste of money, time and human resources that could be better spent pursuing those the government has reason to suspect are a serious threat."

Snowden also defended himself against a Reuters report claiming the former contractor used login credentials and passwords provided unwittingly by colleagues.

"I never stole any passwords, nor did I trick an army of co-workers," he said, disputing the report as "simply wrong."

#AskSnowden Under what conditions would you agree to return to the U.S.? — Jake Tapper (@jaketapper) January 23, 2014

The former contractor, who is currently living in Russia, where he was granted temporary asylum, also dismissed U.S. whistleblower protection laws as too weak to be effective. In reply to a question asked by CNN anchor and chief Washington correspondent Jake Tapper regarding his possible return, Snowden said these laws mean he wouldn't get a fair trial if he were to come back to the United States.

"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, which through a failure in law did not cover national security contractors like myself," Snowden wrote, adding: "This is especially frustrating, because it means there’s no chance to have a fair trial, and no way I can come home and make my case to a jury."

Separately on Thursday, Attorney General Eric Holder said the United States “would engage in conversation” about a resolution with Snowden if the former government contractor accepted responsibility for leaking government secrets but said granting clemency "would be going too far."

Holder mirrored those comments during a public event Thursday at the University of Virginia: “We've always indicated that the notion of clemency isn't something that we were willing to consider. Instead, were he coming back to the U.S. to enter a plea, we would engage with his lawyers. ”

In his final note, Snowden encouraged his readers to contact their respective members of Congress, make their voices heard and push back against unconstitutional surveillance.

Snowden was a contractor when he began leaking details of U.S. surveillance programs to the media last year.

NBC News' Pete Williams and Michael O'Brien contributed to this report.

Related:

Holder: Clemency for Snowden 'too far,' but open to resolution

