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The IWF claims its first study of the number of abusive websites on the internet has turned up around 3,000 sites, with more than 75% run as commercial operations by criminal gangs making money from the images.

"This is the first time any organisation has revealed the true scale of this issue and been clear that the problem is something that can be solved," says IWF chief executive Peter Robbins.

The watchdog's annual report notes that computer networks in Russia and the United States host the most child abuse images and calls for a worldwide campaign by governments, police and the internet industry to investigate and disrupt abusive sites.

"A coordinated global attack on these websites could get these horrific images removed from the web," says Robbins.

Since 2003, less than 1% of child abuse content has been hosted on UK computers, down from 18% in 1997, the report says. Sites hosted in Britain are closed within hours.