Washington ? Earlier this year, one animated character in Second Life, a popular online fantasy world, allegedly raped another character.

Some Internet bloggers dismissed the simulated attack as nothing more than digital fiction. But police in Belgium, according to newspapers there, opened an investigation into whether a crime had been committed.

Then last month, authorities in Germany announced that they were looking into a separate incident involving virtual abuse in Second Life after receiving pictures of an animated child character engaging in simulated sex with an animated adult figure. Though both characters were created by adults, the activity could run afoul of German laws against child pornography, prosecutors said.

As recent advances in Internet technology have spurred millions of users to build and explore new digital worlds, the creations have imported not only their users’ dreams but also their vices. These alternative realms are testing the long-held notions of what is criminal and whether law enforcement should patrol the digital frontier.

“People have an interest in their property and the integrity of their person. But in virtual reality, these interests are not tangible but built from intangible data and software,” said Greg Lastowka, a professor at the Rutgers School of Law at Camden in New Jersey.

Some virtual activities clearly violate the law, like trafficking in stolen credit card numbers, he said. Others, like virtual muggings and sex crimes, are harder to define, though they may cause real-life anguish for users.

Nothing new

Simulated violence and thievery have long been a part of virtual reality, especially in the computer games that pioneered online digital role-playing. At times, however, this conduct has crossed the lines of what even seasoned game players consider acceptable.

Two years ago, Japanese authorities arrested a man for carrying out a series of virtual muggings in another popular game, Lineage II, by using software to beat up and rob characters in the game and then sell the virtual loot for real money.

Julian Dibbell, a prominent commentator on digital culture, chronicled the first known case of sexual assault in cyberspace in 1993, when virtual reality was still in its infancy. A participant in LambdaMOO, a community of users who congregated in a virtual California house, had used a computer program called a “voodoo doll” to force another player’s character to act out being raped. Though this virtual world was rudimentary and the assault simulated, Dibbell recounted that the trauma was jarringly real. The woman whose character was attacked later wept – “post-traumatic tears were streaming down her face” – as she vented her outrage and demand for revenge in an online posting, he wrote.

Since then, advances in high-speed Internet, user interfaces and graphic design have rendered virtual reality more real, allowing users to endow their characters with greater humanity and identify ever more closely with their creations.

Virtual reality, real crimes?

Nowhere is this truer than in Second Life, where more than 6 million people have registered to create characters called avatars, cartoon human figures that respond to keyboard commands and socialize with others’ characters. The breadth of creativity and interaction in Second Life is greater than on nearly any other virtual-reality Web site because there is no game or other objective; it is just an open-ended, lifelike digital environment.

Second Life is intended only for adults, and about 15 percent of the properties on the site – in essence, space on computer servers that appear as parcels of land – have been voluntarily flagged by their residents as having mature material. In some locations avatars act out drug use, child abuse, rape and various forms of sadomasochism.

One user found herself the unwilling neighbor of an especially sordid underage sex club. “Tons of men would drop in looking for sex with little girls and boys. I abhorred the club,” wrote the user on a Second Life blog under the avatar name Anna Valeeva. She even tried to evict the club by buying their land, she wrote.

The question of what is criminal in virtual reality is complicated by disagreements among countries over what is legal even in real life.

Philip Rosedale, the founder and chief executive of Linden Labs, said in an interview that Second Life activities should be governed by real-life laws for the time being.

Rosedale said he hopes participants in Second Life eventually develop their own virtual legal code and justice system.