Pedophiles finding a safe haven on the "dark net"

Sweetie looks and sounds like a young girl from the Philippines.

"My name is Sweetie," she says. "I'm 10 years old."

There are thought to be hundreds of children like her in Southeast Asia, working in front of live Internet webcams, paid to perform sex acts for pedophiles.

But Sweetie isn't real. She's a digital puppet, designed by Hans Guijt and his colleagues at Terre des Hommes Netherlands, a child protection organization, to catch pedophiles.

"In the 10 weeks time that we were active on the Internet we were hit by more than 20,000 people, 20,000 men mainly, who were trying to get in contact with us to engage us in sexual activities," Guijt told CBS News.

But Guijt added that many hardcore pedophiles can't be so easily caught, because they're using a separate, hidden Internet known as the dark net.

Originally developed by the U.S. military, the dark net is only accessible via a browser that masks users' identities by encryption.

The dark net's millions of users -- and thousands of websites -- operate on a network of more than 6,000 computer servers spread around the world that reroute signals to hide users' locations.

It's still partly funded by the U.S. government, in order to help dissidents in China, Russia and Iran evade censorship.

But the layers of security protecting users' anonymity have also made the dark net a haven for pedophiles. While most users employ the dark net browser to hide their IP address while accessing sites on the regular Internet, a recent British study found that 80 percent of traffic to sites located only on the dark net were related to child pornography.

"It was just an awful realization, discovering there were tens of thousands of people who are not only trading child pornography, but planning to exploit children," said Greg Virgin, a former NSA employee turned cyber security consultant, who's now helping U.S. child protection groups.

"We found one site where users openly advertised the ages of the children they were interested in," Virgin said. "The average youngest age they were seeking for girls was zero years old. And the average age for boys was one."

The FBI is believed to have taken down several child pornography sites in 2013, after using malicious software to locate their servers.

Yet Virgin says that failed to stop the dark net's use by pedophiles, which he believes is growing.

"The demand is picked up very quickly by other sites and the sites are replaced very quickly, usually by a stronger, better site."