German police say they have broken up an international child pornography ring with links to thousands of internet users in at least 166 countries.
German police and Interpol have led the operation
Several hundred suspects are being investigated in Germany and more than 500 homes across the country are said to have been searched in the past week.
The BBC's Tristana Moore says this is a major breakthrough for the German authorities.
The operation - known as Marcy - has been going on for more than a year, run by police in the eastern state of Saxony-Anhalt and prosecutors in the city of Halle.
It is being co-ordinated by Interpol and the German federal crime office.
British police have identified 22 suspects with the help of information from the German authorities and are working to identify others.
A spokesman for federal police in Switzerland said dozens of arrests were likely to follow the German-led swoop.
Saxony-Anhalt interior and justice ministries said in a statement that the operation was "the most significant victory" against international child pornography, adding that some suspects were known to police for sex crimes.
"According to the information we now have, many of the suspects are extremely dangerous paedophiles and are from all walks of life," they said.
At a news conference, the authorities said many of the suspects who have been exchanging pornographic images of children on the internet were extremely dangerous.
Teachers, priests and police officers are reported to be under investigation.
Last year, police in Magdeburg carried out a raid on the home of a 26-year-old man who was found downloading images from the internet; investigators then discovered the e-mail addresses of thousands of computer users.
Police said that one man in Bavaria had been found to have 26,000 pornographic images of children.
And in the state of Lower Saxony alone, more than 50 desktop computers and almost 1,500 CD-Roms and more than 200 videos were confiscated.
Distribution of child pornography in Germany carries a jail term of between three months and five years, while possession can incur a fine or a one-year sentence.
The raids follow operations against in five countries in May of this year which led to 21 arrests, including seven in Germany.
The operations were hailed at the time as an excellent example of international law enforcement.