Detectives arrived last summer at a high-rise apartment building in Arlington County, warrant in hand, to nab a suspected pedophile who had traded child pornography online. It was to be a routine, mostly effortless arrest.

But when they pounded on the door, detectives found an elderly woman who, they quickly concluded, had nothing to do with the crime. The real problem was her computer's wireless router, a device sending a signal through her 10-story building and allowing savvy neighbors a free path to the Internet from the privacy of their homes.

Perhaps one of those neighbors, authorities said, was stealthily uploading photographs of nude children. Doing so essentially rendered him or her untraceable.

With nearly 46,000 public access points across the country -- many of them free -- hundreds of thousands of computer users are logging on every day to wireless networks at cafes, hotels, airports and even while sitting on park benches. And although the majority of those people are simply checking their e-mail and surfing the Web, authorities said an increasing number of criminals are taking advantage of the anonymity offered by the wireless signals to commit a raft of serious crimes -- from identity theft to the sexual solicitation of children.

"We're not sure yet how to combat that," said Kevin R. West, a federal agent who oversees the computer crimes unit in North Carolina's State Bureau of Investigation. "Free wireless spots are everywhere, and it makes it easy for people . . . to sit there and do their nefarious acts. The fear is that if we talk about it, people will learn about it and say, 'I can go to a parking lot, and no one will catch me.' But we need to talk about it so that we can figure out how to solve it."

The way it works is simple: Anyone who has a wireless card installed in his or her computer -- and most new computers are equipped with one -- can access the Internet from any of the public WiFi "hotspots," as they're known. In an age of portability and instant gratification, getting online has never been easier -- for law-abiding folks and those with bad intentions.

And in especially dense areas such as the Washington region, some neighborhoods might offer users a dozen or more open wireless signals from which to choose.

"Unsecured networks are a treasure trove for neighbors," said John Sheehan, program manager of the CyberTipline at the National Center for Missing and Exploited Children. "Those looking to access illegal content obviously feel they have anonymity" and can get away with it.

They most often do, authorities said.

"It's frustrating for officers," said Todd Shipley, director of training services at the National Consortium for Justice Information and Statistics. "If a suspect is going from coffee shop to coffee shop and using free signals to commit crimes, the police probably aren't going to catch him. That's the reality."

Open wireless signals are akin to leaving your front door wide open all day -- and returning home to find that someone has stolen your belongings and left a mess that needs cleaning.

One way to combat it is for people to secure their wireless networks by making them password-protected. But, authorities said, businesses and cities that offer free connections need some way to track the users, such as filtering measures that could scan to see who is accessing the network.

Locally, Alexandria recently announced plans to expand its wireless network. The Internet service provider EarthLink will build a citywide network for a 16-square-mile area, with free wireless connections available in more than two dozen public locations. The provider also has worked on municipal WiFi in cities including Philadelphia and New Orleans. Alexandria officials said EarthLink will decide whether to implement security measures on the network, which will be accessible to anyone passing through the city.

In one recent case, West said, a truck driver used free wireless signals at motels across the country to post and view pornographic images of children at a Web site. By pure luck, the man was caught, West said. When the suspect got online from his home computer, authorities were able to trace his computer's Internet Protocol address, or the unique set of numbers assigned to every computer that uses the Internet. That number, which serves as a virtual street address, often leads authorities to the offender's physical residence.

"Otherwise he would've slipped through the cracks," West said. "We wouldn't have been able to identify him."

These days, the Internet is as indispensable to an officer's arsenal as his gun and handcuffs. Indeed, a growing number of officers are being assigned to patrol cyberspace.

Across the nation, 46 multi-jurisdictional Internet Crimes Against Children task forces have been created to carry out online sting operations aimed at ensnaring sex offenders because a man tapping away on a computer in Rockville might very well be soliciting a child in California. Every week, federal and local authorities cast their nets.

And although most sex crimes against underage boys and girls involve victims and suspects who know each other, an increasing number involve online interactions between strangers. Online solicitations -- in which pedophiles cultivate relationships with children and then arrange to meet them in public places -- are becoming more common, federal authorities said.

And even in those cases in which the suspect is brought to police attention by a neighbor or friend or relative, computers are often rich sources of evidence, West said.

"Technology just makes the park no longer the only place where the pervert goes," West said.

The Northern Virginia-D.C. task force has officers from 23 local, state and federal agencies. It was established in November 2004 through a grant from the Office of Juvenile Justice and Delinquency Prevention at the Justice Department. Since its creation, dozens of cases have been opened and more than three dozen arrests have been made.

Those assigned to the task forces patrol the virtual streets for pedophiles and others who want to commit crimes against children. Using software and other tracking devices, the officers trace a suspect's IP address. But as technology improves, so too do the tactics of criminals. Closing cases is more difficult if the IP address originated from a wireless signal because it often leads back to the owner of the network instead of the criminal.

The problem is going to get worse, authorities said. Every day, more homes, businesses and entire jurisdictions are outfitted with wireless networks, creating an almost seamless patchwork of available Internet connections to anyone with a laptop and the desire to get online.

"This is part of the future . . . and we're working to catch up and educate the public," said Capt. Tommy Turner of the Virginia State Police.

About the Author

By Jamie Stockwell Washington Post Staff Writer Sunday, February 11, 2007; Page C01 http://yahoo4youbuy.blogspot.com http://rosevalentine.blogspot.com