Screenshot by CNET/"Last Week Tonight with John Oliver"

A generational change could help usher in a new era in which governments prune back their surveillance efforts.

That's the message from the American Civil Liberties Union, drawing on a study that looked into the attitude of millennials in 10 countries toward Edward Snowden, who in 2013 leaked reams of classified documents about spying programs conducted by the US National Security Agency. What the ACLU found, it said, is that members of this younger generation who know about Snowden have an "overwhelmingly positive opinion" about him.

Millennials -- those born roughly between 1980 and 1999 -- also tend to believe that Snowden's disclosures will help to bring about greater privacy protections, according to the ACLU.

"The broad support for Edward Snowden among millennials around the world should be a message to democratic countries that change is coming," Anthony D. Romero, executive director of the ACLU, said in a statement Tuesday. "They are a generation of digital natives who don't want government agencies tracking them online or collecting data about their phone calls."

One of the earliest and most startling revelations from the NSA documents concerned the agency's sweeping collection of telephone records for domestic calls in the United States. Another program, known as Prism, focused on monitoring Web data.

The ACLU published the results of the survey as a June deadline draws near for the US Congress to vote on whether to renew the Patriot Act. At least one provision of that national security legislation -- Section 215 -- has been used by the NSA as justification for its collection of US telephone records. Technology companies including Google, Facebook, Twitter and Apple have called on the US government to reform its surveillance efforts, including putting an end to bulk collection of data.

The civil liberties group also pointed toward efforts in a number of countries around the world, including the Netherlands, France and Canada, to expand their own surveillance programs.

But in those and other democracies, the ACLU said, millennials are going to make up a sizable portion of votes in the coming years, and their attitudes against surveillance could spell trouble for governments seeking more of it.

"Efforts to rein in government surveillance are inevitable given the sure rise of the millennial generation and its broad support for Edward Snowden," said Romero, who also took to the op-ed pages of the LA Times to make his case. "Old folks just don't get it. The new generation will fix it if we don't."

The ACLU survey didn't offer any tally of the attitudes of older generations, focusing instead on respondents between the ages of 18 and 34. The study, conducted online over the course of one week in February, drew on the responses of approximately 1,000 adults in each of 10 countries -- the US, Canada, Australia, New Zealand, Britain, France, Germany, Italy, the Netherlands and Spain.

From opinions on Snowden himself to views on whether he's a catalyst for change, US millennials are far behind their counterparts in Europe, according to the survey.

For instance, while 86 percent of millennial respondents in Italy viewed Snowden positively, and 85 percent in Germany, US millennials came in dead last, with 56 percent of respondents saying they had at least a "somewhat positive" view of Edward Snowden.

US-based millennials were also generally negative on Snowden's impact on the country's national security, with 36 percent saying that his leaks hurt national security, compared to 29 percent saying his leaks helped. Millennials in every European country, plus Canada and New Zealand, tended to think Snowden's leaks help national security rather than hurt it. US millennials also felt that Snowden's leaks do "more to hurt" global efforts to prevent terrorism than help them.

Last month, an Amnesty International survey in 13 countries showed a wide range of popular opinion on the benefits, risks and appropriateness of government surveillance.

Since the leaked NSA documents started to hit the Web, Snowden has been on the run, seeking asylum from US government agencies that revoked his US passport and sought his arrest. For the last year and a half, he has been living in Russia.

The ACLU's study, which shows that American millennials are less likely to know about Snowden than their counterparts in other Western countries, echoed the more casual findings of HBO's comedic news show "Last Week Tonight with John Oliver." In an episode of the show that aired earlier this month, Oliver interviewed Snowden at length in Russia and also played snippets of man-in-the-street interviews in the US in which people were asked if they knew who Snowden was. Nearly all of them guessed incorrectly, with some positing that he might be Julian Assange, the WikiLeaks editor behind a separate revelation of confidential US military and diplomatic documents.

Despite a greater preponderance of concerns and negative views among US respondents, the ACLU, which supports Snowden and has called on the US government to offer him clemency, said the data showed a clear, positive direction for handling of surveillance worldwide.

The organization did find in the survey that 40 percent of US millennials believe Snowden's leaks "will lead to more protection" of privacy rates, compared to 24 percent of respondents who said the leaks would translate to "less protection."

"The government will look back in shame at its effort to prosecute Snowden for blowing the whistle on the NSA," Romero said. "I don't think there is any doubt that Snowden will inevitably take his rightful place in U.S. history as a whistleblower and patriot."

The ACLU did not respond to a request for comment.