Anonymous text messages are one way that technology can help veil identity.

Despite the proliferation of look-at-me sites like Facebook and Twitter, which are places that encourage the phenomena known as “oversharing,” technology’s most powerful allure may be how it empowers anonymous users to delve into taboo topics, subvert government efforts to control information and engage in behavior frowned on by polite society.

Some American teenagers, for example, likely too embarrassed to address their most intimate questions to their parents or peers, can now turn to their cellphones for help. In North Carolina, a service that started February 1 is staffed with counselors who will answer anonymous questions by text message.

“Technology reduces the shame and embarrassment,” Deb Levine, executive director of ISIS, a nonprofit organization that began many technology- based reproductive health programs, told Jan Hoffman of The New York Times. “It’s the perceived privacy that people have when they’re typing into a computer or a cellphone. And it’s culturally appropriate for young people: they don’t learn about this from adults lecturing them.

Beyond sex education, information is among the hottest online commodities. But more than 20 countries now use blocking and filtering systems for Internet content, according to Reporters Without Borders, a Paris-based group that encourages freedom of the press. The most aggressive filtering systems are used by authoritarian governments like those in Iran, China, Pakistan, Saudi Arabia and Syria, according to a Times article by John Markoff.

The government often succeeds at controlling information, but some ordinary citizens have found a way to elude the online censors and shield their identities.

Last year, a free download allowed up to 400,000 Iranians to surf the uncensored Web, according to a Times article by John Markoff. The software was developed by supporters of the Falun Gong, a spiritual movement suppressed by the Chinese government since 1999.

Shiyu Zhou, a computer scientist, is a founder of the Falun Gong-affiliated group that developed the software. After the Chinese government cracked down on pro-democracy activists in Tiananmen Square in 1989, Shiyu said he understood the power of government-controlled media when the nation’s student protesters were transformed from heroes to killers. “I was so disappointed,” Mr. Shiyu, a college student at the time, told Mr. Markoff. “People believed the government, they didn’t believe us.”

Beyond lusty teenagers and citizens seeking unfettered information, though, is a darker online world where sexual favors are traded like used books on Ebay.

Two recent encounters arranged in the United States on the free online site Craigs list resulted in grisly killings. Craigslist said it would close its erotic services category; its new adult services category, it said, would be monitored.

But it seems unlikely that the online marketplace for sex will change, mostly because of demand.

Erick Janssen, a researcher and associate scientist at the Kinsey Institute for Research in Sex, Gender, and Reproduction, said that some need sex and sexual novelty more than others. “We know from basic sex research,” he said in a Times article by Douglas Quenqua, “that anonymity can augment satisfaction in sexual arousal.”