In a new report, the United Nations reveals the scale of the problems of humans trafficking and sex slavery around the world.

Outside view of a club in Estonia, the only European Union country without a law covering human trafficking. (Timur Nisametdinov /AP)

The operators of the networks, who the U.N. report says make $32 billion a year, are based around the world — including in the United States.

The U.S.-based classifieds site has come under fire for human trafficking advertisements in their adult services section.

Village Voice Media, which runs the site, has repeatedly said that it makes every attempt to weed out traffickers and that if traffickers do make it to the site, law enforcement can use the site to find them.

A request for comment from VVM was not immediately returned.

New York Times columnist Nicholas Kristof published a scathing piece about last month, writing:

“Backpage accounts for about 70 percent of prostitution advertising among five Web sites that carry such ads in the United States, earning more than $22 million annually from prostitution ads, according to AIM Group, a media research and consulting company. It is now the premier Web site for human trafficking in the United States, according to the National Association of Attorneys General. ”

VVM responded to the article by detailing the automatic and human filters it uses to keep out traffickers and wrote that “for the first time in the history of sex work, law enforcement has, because of the Internet, the ability to shine a light upon those who would abuse children.”

Nevertheless, the company has continued to draw criticism, including in a recent article in the Daily Beast and from John Buffalo Mailer, the son of Voice cofounder Norman Mailer,

Human trafficking occurs worldwide. The State Department annual report on trafficking in persons details how bad the problem is in each country. Estonia, for example, is the only European Union country without a law covering human trafficking.

Listen to Secretary of State Hillary Rodham Clinton discuss trafficking around the world, below: