In late 2007, Carlos Miguel Sobral and 14 other Brazilian police investigators were getting ready for another day of fighting Internet crime when one of them suggested looking into peer-to-peer file sharing networks.

Sobral said the other federal investigators agreed, choosing to focus on eMule, Brazil's most popular file sharing program.

The investigators soon saw that the network was being used to distribute child pornography, not just in Brazil but around the world, Sobral told The Associated Press on Friday. "We then developed our own software to identify those individuals using eMule for this purpose."

The result unleashed a worldwide investigation involving Interpol that has led to the arrests of hundreds of alleged child pornographers in Europe, the United States, Australia and Latin America, and it promises to send many more to jail.

"The recent arrests in Australia and other countries are a direct result of our Operation Carousel, which we set in motion in December 2007 as part of our routine efforts to combat the criminal use of the Internet," said Sobral, who heads the federal police department's cybercrime unit.

The investigation focused on men sharing images over the Internet — peer-to-peer file sharing — rather than downloading from an illicit Web site, which is easier to detect.

On Thursday, Australian detectives charged 22 men including a policeman, a senior lawyer and a child care worker in connection with the global child pornography-sharing network.

Australian Federal Police Deputy Commissioner Andrew Colvin acknowledged that the operation was prompted by information from Brazilian investigators shared via the international police agency Interpol. He called the images some of the worst that Australian police had ever seen.

Sobral said Brazilian police identified some 250 people in at least 78 countries, leading to the arrest of suspects in nations such as Australia, Spain, Israel, Greece, Japan, New Zealand, Portugal, Lithuania and Brazil.

Until recently, possession of child pornography was not a crime in Brazil, but distribution was, which is why "of the nearly 200 people detained in Brazil as a result of Operation Carousel, only five are in jail."

"It is very difficult to catch someone in the act of distributing porn," Sobral said.

But last month Brazil approved a law making possession of child pornography a crime punishable by up to eight years in prison "and this means that from now on we should be making a lot more arrests," Sobral said.