Australian police have arrested 70 people and removed four children from their homes in a six-month nationwide investigation of a global child pornography network, officials said Thursday.

Twenty other people have been summoned to appear in court. All 90 — including a police officer and several teachers — face charges of accessing images of child abuse on the Internet, police said.

Australian Federal Police Commissioner Mick Keelty said the Interpol-led investigation was conducted simultaneously by law enforcement authorities in 170 countries. Further arrests are expected, he said.

It was one of the largest child pornography investigations in Australian history, police said.

The investigation was triggered after a hacker posted 99 child porn images on a European Web site, which attracted 12 million hits in just 76 hours, including 2,800 from Australian computers, police said.

Federal police assistant commissioner Andrew Colvin said 1,500 people or computers in Australia had been identified so far through their Internet Protocol, or IP, addresses.

Thousands of DVDs of child pornography and dozens of computers have been seized in the investigation, he said.

The children in the images range from babies to 18 years of age. Some images show rapes and other abuses, Keelty said.

"These are not children in passive positions. These are children who are being abused," he told reporters. "The real tragedy of this is that we don't know the origins of a lot of these children. We don't know whether these children are still being the victims of child abuse."

Police said four children who are dependents of alleged offenders were removed from their homes for their safety, but could not confirm whether they appeared in any of the seized images.

Possession of child pornography carries a maximum penalty of 10 years' imprisonment.