British police arrested more than 70 people and seized computer equipment on Wednesday morning in what is thought to be the UK's largest-ever crackdown on Internet paedophiles.
Thirty-four police forces across the UK took part in the operation, which was code-named Magenta. It followed a six-month joint investigation involving officers from Hertfordshire Constabulary and Greater Manchester Police.
Operation Magenta had traced people who were using Internet chatrooms to swap sexually explicit images of children, police said.
Officers explained that the large number of arrests showed that the police were committed to apprehending those who possess and distribute indecent images of children.
"Today's nationwide operation should send out a loud message to those people who use chatrooms to trade in indecent images of children. This activity is unlawful and is committed by people who often go on to commit further offences of abuse against vulnerable children," said Inspector Keith Tilley, of the Hertfordshire police force.
More details of Operation Magenta are expected to be released later on Wednesday.