RIO DE JANEIRO, Brazil — The harried mother had little wish to visit an internet cafe with two squirmy boys in tow, but she said there was no choice.

New to this potholed neighborhood on the city’s northern edge, Fabina da Silva, 31, needed to enroll her sons in school. Registering online was the only way.

“If it wasn’t a necessity, I wouldn’t be here,” da Silva said on a recent afternoon as her 6-year-old, Lucas, thumped his toy Sponge Bob on the mouse pad beside her. “Nowadays, internet in Brazil is a necessity.”

Brazil has long been a bellwether nation for emerging-market internet trends and it’s riding a wave that will soon sweep the globe. The newest billion people to venture online are doing so in developing countries rather than North America or Europe.

And whether those newcomers are getting online for fun or because they must, they’re doing so en masse. For businesses nimble enough to serve markets as diverse as Brazil, Russia, India, China and Indonesia, the shift promises a staggering number of new customers.

But internet trend-watchers say there’s more at stake than the emergence of a worldwide class of digital consumers. The new users are changing the culture of the internet itself. Researchers say the web as it was originally, if idealistically, conceived — a largely free, monolingual space where a shared digital culture prevailed — may soon be a distant memory. And it’s happening remarkably fast.

“Potentially explosive” is how Marcos Aguiar describes the growth. He’s a senior partner at the Boston Consulting Group’s Sao Paulo office who co-authored a report released in September called “The Internet’s New Billion.” It concludes the number of web users in developing-world “BRICI” countries — Brazil, Russia, India, China and Indonesia — will jump from 610 million this year to 1.2 billion by 2015.

When the internet crossed the billion-user threshold just five years ago, the developed world commanded a 60-40 majority online, according to the United Nations’ International Telecommunications Union. Today, that proportion has roughly reversed.

The new users are younger, poorer and more numerous than ever before, BCG’s analysts said, and increasing numbers will need web access and won't be able to afford broadband in their living room.

As Fabina da Silva pecked away on a keyboard to register her sons for school, she was in many ways typical of low-income Brazilian users. Those who don’t have web access at home often pay small fees to use ad hoc cybercafes known here as “LAN houses.” Many began as rooms full of connected computers, or local area networks, for multi-player gaming, but their customer base has since broadened.

In India, those following the trend say a huge portion of the new billion will enter the web via mobile devices.

“If you look at our broadband figures in India, it’s quite pathetic,” said Sunil Abraham, director of the Centre for Internet and Society, a think tank in Bangalore. “And less than 1 percent of the population has ever accessed the internet.”

But recently, many Indian telecommunication firms have begun giving out free data plans with their mobile devices — a move Sunil said will instantly send millions of Indians onto the internet. “The moment an end user acquires a smart phone they become a data user because they’re not paying for it,” he said. “But they’re not coming onto the internet like you and I know.”

Instead, phone companies only provide access to a few sites, such as Wikipedia and Facebook Zero, a stripped-down mobile version of the social networking site that omits photos but allows messaging and status updates. “They’re coming onto a network that, from the beginning, is a complete walled garden,” he said.

The new walls dividing regions of the internet aren’t likely to stop there. Even as more users join the web worldwide, they are increasingly separated by language. What the nearly 400 million users in China experience as the internet is vastly different than the web surfed by Americans. Much of the software and websites on the Chinese web are produced domestically in the local language. That’s also how it works in Russia and Indonesia.

Some observers say this difference has political consequences. “Many of the local companies provide far better service than the likes of Google and Facebook in those markets,” said Evgeny Morozov, a digital technology researcher at Stanford University. “But also those local websites are much easier to censor because the corporate entities behind those sites all have some domestic presence.”

Morozov is author of an up-coming book “The Net Delusion: The Dark Side of Internet Freedom,” and he said there’s a dark side to be found in the internet’s new billion, too. Because poorer users resort to more centralized methods for getting online — cybercafes, cell-phone towers — their activity will be much easier to monitor.

“The fact that so much of this is happening in cybercafes and mobile devices actually empowers the government because those two things are much easier to control than a desktop computer in your house,” Morozov said.

Morozov is also skeptical of notions that greater diversity of cultures online will lead to more cultural dialogue. “There is very little interaction between communities and it’s not because the tools are lacking. It’s just that modern-day Indians and modern-day Russians have nothing to talk about most of the time,” he said. “There may simply be no demand for joining that global village.”

More optimistic web scholars argue there will be cultural conversations, but bridging the gaps between communities will take effort. “The internet has become a bunch of interlinked but linguistically distinct and culturally specific spaces,” said Ethan Zuckerman, a senior researcher at Harvard University’s Berkman Center for Internet and Society. “There’s some interface between them but there’s a lot less than there was years back when we were sort of pretending that this was one great global space.”

Instead of becoming the world’s biggest tool for cultural exchange, Zuckerman said the web could become its principal medium for mutual misunderstanding. “We’re mostly talking to people like ourselves rather than talking across cultural boundaries,” Zuckerman said. “And when we do cross cultural boundaries, it’s often in a way where we’re overhearing something that really pisses us off.”

Take for example the 2005 scandal after a Danish newspaper posted cartoons depicting the prophet Mohammed, sparking riots across the Muslim world. Zuckerman said such incidents may become routine. “It’s a problem of unseen audiences,” he said. “We always have to be aware there are other audiences out there listening, and they’re particularly listening for mentions of themselves.”

For a more amusing and recent online snafu, Zuckerman prefers citing a topic that went viral on the micro-blogging site Twitter this summer. The topic, the Brazilian Portuguese phrase “Cala boca, Galvao,” was mysterious to many English-speaking users. Asked to explain, a few mischievous Brazilians claimed the Galvao was a rare Amazon bird being slaughtered to extinction for its colorful feathers. For everyone who re-tweeted the phrase, so the pranksters claimed, 10 cents would be donated to a global effort to save the bird.

The encouragement helped catapult the phrase into the ranks of Twitter’s top-trending topics, or most-repeated phrases worldwide last June. But in reality, Galvao was the first name of Galvao Bueno, a Brazilian sports commentator on the Globo network, whose pronouncements during the World Cup had irritated many of his compatriots. In Brazilian Portuguese, “Cala boca” roughly means, “shut up.”

“There’s an entirely different conversation going on that’s so incomprehensible to Americans that the Brazilians make fun of us when we try to understand,” Zuckerman said. “In many ways that sort of characterizes for me what’s going on with the contemporary ‘net.'”

But Zuckerman still believes virtual borders can be crossed. In 2005, he co-founded Global Voices, an aggregator and translator of blogs from around the world, in part to help the next billion web users communicate.

“These billion users are sort of proxy for the global middle class,” he said. “They’re an increasing economic force, an increasing cultural force, and they are the people we need to negotiate with and have a conversation with if we want to address problems like climate change.”

In the run-down Engenho da Rainha neighborhood in Rio de Janeiro, some of the LAN house customers seemed more interested in using the web to play games than solve the world’s problems.

One wiry teen in a blue baseball cap barely glanced away from his screen to answer questions. “I’ll spend all day, all night on the internet if I’m allowed,” said Carlos Wallace Cruz, 16. “I’d say I’m 98 percent addicted.”

Cruz’s drug of choice isn’t likely to ring a bell with Americans his age. It’s a video game available only on Orkut, a Google social networking site, wildly popular in Brazil and India but less so in the United States.

When a visitor asked if he ever spent time on Orkut’s much more famous rival site, Cruz responded with earnest puzzlement.

“What’s Facebook?” he asked.

