LinkedIn is a network for all professions — even the oldest one.

The social network this week updated its policies to keep prostitutes from plying their trade on a site, warning users not to “create profiles or provide content that promotes escort services or prostitution.” The rule even applies to those in Nevada, the only U.S. state to legalize prostitution in brothels. In fact numerous employees in Nevada of brothels like the Moonlite Bunny Ranch and The Dovetail Ranch have LinkedIn profiles. Another advertised “nude massage,” “escort” — and “academic work.” As of Wednesday, 314 people listed “prostitution” as a skill on the site, although most appear to be in law enforcement careers.

LinkedIn: Prostitutes not welcome

But LinkedIn US:LNKD isn’t the only social network having to deal with sex workers. Red light districts are no longer cordoned off online, but seem to thrive in plain sight on Facebook FB, -3.30% and Twitter, experts say.

See: LinkedIn: Prostitutes Not Welcome.

A cursory search of Twitter and Facebook also turns up profiles for alleged escort agencies. Facebook policies don’t mention prostitution, but the site prohibits fake profiles, pornography and illegal activity. “We encourage people to report anything they find offensive or misleading,” a company spokesman says. Content that violates Facebook’s guidelines and terms will be removed, he says. (LinkedIn and Twitter did not immediately respond to requests for comment.)

Tackling prostitutes on social networks, however, is not as easy as cleaning up New York’s Times Square or closing down a red light district in a small town. LinkedIn has 225 million members worldwide, Twitter has 200 million registered users, and Facebook has 1.1 billion unique monthly visitors. Profiles can be deleted as easily as they are set up. What’s more, some listings on LinkedIn used obscure titles like “Independent Entertainment Professional” to refer to things other than clowns or magicians for children’s birthday parties.

Sex has always driven technological innovation, says Patchen Barss, author of “The Erotic Engine,” from cave drawings to VHS tapes to photo-sharing sites. In fact, some Victorian gentleman carried pornographic “Stanhope microphotographs” in their pocket watches. “The same is true for carrying e-books today,” he says. “It’s like wearing kinky underwear.” When “Fifty Shades of Grey” was released in 2012, for instance, the e-book initially sold six times faster than the printed version.

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For better or worse, sex workers moving from seedy sex sites to social networks makes prostitution appear more accessible and acceptable to middle- and upper-income groups, experts say. “Studies suggest that professional men looking for quick sexual encounters use social networks because it’s safer, since it’s largely invisible to police and offers a way to select and prescreen women,” says Ashley Mears, assistant professor of sociology at Boston University. “I wouldn’t say it’s a matter of going mainstream, but rather class segmentation.”

It’s part of a cultural shift. Governments have cracked down on street-level prostitution to clean up cities and make them more tourist and business-class friendly, which has driven more sex workers online, Mears says. “Street-level sex workers are at the greatest risk of violence and policing,” she says. “So only the most economically desperate women take to sex work on the streets.” Male and female sex workers with smartphones, Mears adds, can easily set up profiles on social networks or location-based mobile-dating sites.