Cox was the ringleader of a chat room called “Kids the Light of Our Lives,” which allowed users to trade and watch live images of children being abused through file sharing and video streaming. “No investigation has rescued so many young and vulnerable people from a group of hard-core pedophiles,” says Jim Gamble, who heads Britain’s Child Exploitation and Online Protection Center (CEOP). There have been several other indictments, including the jailing last week of a man from Manchester who will serve seven years for child rape and a British music teacher, jailed in April for persuading young girls to strip in front of Web cams. Bill Thompson, a technology expert who teaches courses in electronic media at London’s City University, spoke to NEWSWEEK’s Ginanne Brownell about the technology that led to these arrests. Excerpts:

NEWSWEEK: How did police find this ring? Bill Thompson: In 2005 the cops in Canada arrested someone in Edmonton. Following that they were able to infiltrate two chat rooms in the U.S. that were being used. They found out about Timothy Cox because he was part of that community of pedophiles. You often hear about how police can tap our e-mails and look at what sites we are visiting, but often they get a lucky break in one case and that leads them to other people. So this was human intelligence.

How did they find all the others who were involved? Well from what we can understand by reading between the lines—the police do not, of course, want to give too much away—they arrested him when he was away from his computer; they then went to his home and logged on as him and pretended to be him for 10 days. They gathered IP addresses and whatever details they could get to allow them to trace back to the others. So what that implies to me is that what this guy had set up was a private chat room running on his computer—he was administering it. It was not a public Web site, it was a piece of chat-room software, so you needed to know it was there, you needed to know the IP address, you needed to know a username and password. It would not be indexed by Google or anyone like that, not visible to the outside world. And from hints in what the police were saying, I suspect that once people made contact they were not actually sharing files directly from the chat room, they were sharing files by using things like instant messaging file transfer, peer-to-peer programs, Skype. Nearly every interactive program from MSN or whatever allows you to move files around. What people would do was establish contact through his chat room and trade images. They have not said that, but it is a strong implication that that is what was going on. How do people find these sites if they are password protected? I suspect it is different for different people. Some people maybe go to Google and are searching for images and find stuff of younger and younger children. They eventually find a Web site which offers child abuse. There is an e-mail address, someone who will then check you out before letting you know the full details. And the checking out is that you have to have stuff to trade. So you provide images of child abuse to them, which is a criminal act, and then once you are into the site there will be levels of access, levels of privilege. You become more and more trusted over time. One of the great things about this sting operation is it will worry everyone. Because anyone who is in one of these communities now is going to say, “Well actually one of the people I am talking [to] could now be a police officer. Maybe I have actually made a mistake.” So it could well have a significant deterrent effect. It will stop people trading because they will no longer trust the people at the other end.

Is this the first time where the police did what they did—went on masquerading as a suspected perpetrator? It is the first time I have heard about them doing this. That does not mean it is the first time it has been done. [The police] may have decided to go public as a strategy, a tactic. It is an obvious thing to do.

Did advances in technology on the Web have anything to do with this? In this context, no. Nothing that was done on this operation could not have been done 10 or 12 years ago. What changed I suspect is that police now are more clued up on how to do it.

Is this going to make it trickier for pedophiles? Yes, it will. Say I am interested in trading child abuse. Now I am going to look at ways for doing identity verification for the person on the other end of the line. So for example with Web cams, if I have been talking to you for six months and I ask you to come up on your Web cam and you won’t, I know there is a policeman there. You can imagine well-organized groups will start using technologies which will make it harder for police to take over someone’s identity. There will be more done on the part of these people to keep themselves more secret. That is unfortunate, but it also means it will be harder to [be] accepted into the circle. The end result should be fewer images being traded by fewer people—but then the hardened people who have been doing this for some time will be harder to track down.