RIO DE JANEIRO Ask Internet users here what they think of Orkut, the two-year-old Google social networking service, and you may get a blank stare. But pronounce it "or-KOO-chee," as they do in Portuguese, and watch faces light up.

"We were just talking about it!" said Suellen Monteiro, approached by a reporter as she gossiped with four girlfriends at a bar in the New York City Center mall here. The topic was the guy whom 18-year-old Aline Makray had met over the weekend at a Brazilian funk dance, who had since found her on Orkut and asked her to join his network.

Orkut, the invention of a Turkish-born software engineer named Orkut Buyukkokten, never really caught on in the United States, where MySpace rules teenage cyberspace. But it is nothing short of a cultural phenomenon in Brazil.

About 11 million of Orkut's more than 15 million users are registered as living in Brazil — a remarkable figure given that studies have estimated that only about 12 million Brazilians use the Internet from home. (And that 11 million does not include people like Ms. Makray, who clicked on Hungary as a nod to her heritage, or someone named Mauricio who wrote in Portuguese but jokingly registered as being from Mauritius.)

Expect Brazilian Portuguese dictionaries to add "orkut" to upcoming editions. O Globo, Rio's biggest daily newspaper, refers to it without further explanation. And the Brazilian media routinely measures the popularity of music groups and actors by the number of user communities dedicated to them on Orkut.

"Surto," a popular comedic play showing in Rio de Janeiro, is peppered with references to Orkut. And the site's jargon has entered the Brazilian lexicon, like "scrap" (pronounced "SKRAH-pee" or "SHKRAH-pee"), meaning a note that one user leaves in another's virtual scrapbook for everyone — including jealous boyfriends and girlfriends and curious suitors — to see.

But the sheer popularity of Orkut, which people can join by invitation only, has had several unexpected consequences. Almost as soon as Brazilians started taking over Orkut in 2004 — and long before April 2005, when Google made Orkut available in Portuguese, English-speaking users formed virulently anti-Brazilian communities like "Too Many Brazilians on Orkut."
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In general, though, Orkut fanatics seem undisturbed by illegal activity on the site, which most of those interviewed said they had never come across personally. They were more interested in finding long-lost classmates and friends, one of the site's most lauded abilities. Schools, workplaces, even residential streets have "communities" joined by people who have studied, worked or lived there.

And everyone has stories of romance foiled by a telltale posting. Ms. Makray once found the page of a man who had flirted with her in a club. "He hadn't told me that he had children or that he was married," she said. "I discovered it on Orkut."

Erika Laun, 23, checks Orkut every day from work to keep an eye on her boyfriend. "When we were first going out," she said, "a girl who liked him was always sending messages and making fun of the messages that I sent him." The rival's sister, whom he didn't even know, helped out, sending messages like "Hey big boy, love you, 1,000 kisses."

"I was really angry," Ms. Laun said.

No one quite knows why Orkut caught on among Brazilians and not Americans, although the fact that it is an invitation-only network might explain why it exploded in Brazil. In a 2005 interview with the newspaper Folha de São Paulo, Mr. Buyukkokten said it might be because Brazilians were "a friendly people," and perhaps because some of his own friends, among the first to join the network, had Brazilian friends.

Fernanda Leon, an architecture student eating at a Middle Eastern restaurant here with her boyfriend, said she thought Brazil had gravitated toward Orkut because of the country's inherently social culture. "Brazilians really want to interact with other people, both old friends and new people," she said. She has 379 friends on her network.