The operation is said to be the largest ever of its kind in Spain
Spanish police says they have arrested 121 people in the country's "biggest-ever operation against child pornography on the internet".
Millions of images that show child sex abuse were seized in a series of nationwide raids, which uncovered a network spanning 75 countries.
Police say two of those held were using their own children to make pornography.
A further 96 people have been charged with possession and distribution of child pornography.
The arrests, made over the past seven days, were part of a long-term operation which began in July last year with the help of Brazilian police.
Those detained include bank clerks, porters and airline pilots, and some are foreigners resident in Spain.
About 800 officers were involved in conducting 210 searches in 42 different provinces that "seized millions of archives of videos and photographs some of which show extremely harsh abuse of minors", police said.
In addition, 347 hard drives, 1,186 CDs and DVDs and 36 laptops were seized.
Enrique Rodriguez, from the police's Technological Investigation Brigade, told Spanish radio that the network was enormous, involving 18,000 IP addresses across the world, including 1,600 in Spain.
IP addresses are unique numbers that identify each computer connected to the internet.
Police say the foreign leads will now be followed up through Interpol.
The raids bring to 1,200 the number of people arrested for child pornography in Spain over the past five years.