Federal Police Commissioner Mick Keelty gave details of the investigation
Seventy people have been arrested in Australia in a nationwide operation to crack down on the use of images of child sex abuse posted on the internet.
The arrests, which include a policeman and several teachers, followed a six month investigation by police into paedophile communities online.
The probe was launched after 95 explicit pictures were posted by a hacker on a respected European website.
Over 76 hours, the site had 12 million hits from 150,000 users in 170 nations.
More than 2,800 internet protocol (IP) addresses were traced back to Australia and then identified by police.
The first arrests were made in cases where young people might be at risk and four children had been taken from their homes, investigators said.
Australian Federal Police Commissioner Mick Keelty said that the probe was ongoing and there would be more arrests in the coming days.
Investigators had worked both with international partners and state police in what Mr Keelty described as one of Australia's largest single operations against images that show child sex abuse.
"In Australia the operation has netted over a million images of children, and these are not children in passive positions, these are children who are being abused," he said.
Correspondents say that the operation has highlighted the increasing sophistication with which paedophiles trade images online.
In the latest case, temporary chat rooms - which suddenly appear and then close almost as quickly - were used to pass on details of the location of the images.
Previous cases have shown that legal photo album websites are an increasingly common way for abusers to trade images.
Some commercial child abuse websites, run by criminal gangs, break up images on to several servers around the world. The fragments, like pieces of a jigsaw, are only united when a paedophile downloads an image.
Other websites or chat rooms only appear on the web for a short period of time, or move servers regularly to different legal jurisdictions.
And the latest technology, such as web-enabled devices like the Sony PlayStation and new generation mobile phones, is being used to download these images.
A spokesman for the UK's Child Exploitation and Online Protection Centre told the BBC: "Whilst this may not be run-of-the-mill it's not surprising that they're using these tactics to trade images.
"They're using all types of technology.
"They use websites, they use newsgroups, online communities, peer to peer networking; they're looking to exploit all means possible."
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