U.S. law enforcement calls it a loophole big enough to throw a desktop through, and about as frustrating.
But some free speech advocates say the issue is overblown, because no actual crime is being committed, at least according to U.S. law.
They're talking about "virtual child porn," the computer depiction of adults having sex with children. It has found a home at places like the popular Second Life game, which is available online.
Many child advocates see it as the most troubling manifestation of child sex abuse that's come along in years.
And they blame a 2002 court ruling that tossed out a law that made it illegal.
Last week authorities in Germany — where virtual child porn is a crime — launched an aggressive investigation to track down anonymous video game users who created virtual child porn on Second Life.
That wouldn't have been the case in the United States, where in 2002 the U.S. Supreme Court ruled that large sections of the 1996 Child Pornography Prevention Act, including the depiction of virtual child porn, were overly broad and unconstitutional. Free speech advocates and pornographers had challenged the legality of the act, and six of the nine justices sided with them.
Then-U.S. Attorney General John Ashcroft was furious, saying the ruling would make it "immeasurably more difficult" to investigate and prosecute pedophiles and child pornographers. In an unusually blunt public rebuke to the court, the Justice Department ordered that all pending child porn cases be reviewed to see whether the defendants could be prosecuted under broader obscenity laws.
"It's very disturbing for child advocates because it's sort of [a] loophole," said Brad Garrett, a former FBI agent and an ABC News consultant.
Another agent, who worked for the FBI's Innocent Images Task Force, told ABC News he was "devastated" by the ruling.
"I still can't can't believe it," said the former agent, who declined to be identified because he is not authorized to talk about his work with the agency. "All virtual porn does is satisfy [pedophiles] until they can find their next victim. It feeds their addiction."
As computer technology gallops rapidly into uncharted territory, interactive, or "open source," video games have allowed some users to break or subvert gaming rules and create virtual child porn — the virtual depiction of an adult having sex with a child.
"There are increasing numbers of cases in which people charged with child porn related offenses are arguing … that the children in the images aren't real," said Ernie Allen, president of the National Center for Missing and Exploited Children. Working closely with law enforcement agencies nationwide, Allen's agency has for years been at the forefront of efforts to track and catch pedophiles.
"We believe that the kinds of images included in 'age play,'" cyberspeak for online sexual fantasies with minors and young people, "are an increasing phenomenon and will be a growing concern," Allen said.
But like many others who spoke to ABC News about the vexing problem virtual child porn poses to U.S. law enforcement, Allen was realistic.
"The first and primary focus is protecting real children against this horrible abuse," he said, "but this is a problem that is coming."