Some 75 people across Europe have been arrested for allegedly sharing images of children online, according to Europe's policing agency.
"Operation Daylight" was launched last year after Europol received information from Swiss police about a vast network trafficking in the sexual exploitation of children. All told, the investigation covered more than 200 cases, according to Europol spokeswoman Claire Georges.
"The investigation lasted for more than a year, based on the Swiss information which led to 611 'intelligence packages' being sent to 26 EU member states," she said. Norway and Switzerland also participated.
So-called intelligence packages provided detailed information about suspects and could for instance include computer information such as IP addresses, Georges said.
The perpetrators frequently used the "dark web" and the Tor encryption system required to access it to mask their identities, she added.
These pedophile networks "continue to be a primary source for persons with a sexual interest in children who are seeking child sexual abuse and exploitation material online," according to a Europol statement released from its headquarters in The Hague.
Europol did not mention specific countries, but Italian police issued a separate statement saying that many of those arrested were unknown to law enforcement as potential criminals.
"All above suspicion and many of them older than 50, they secretly contributed to this despicable network from the confines of the four walls of their homes, always paying maximum attention to source the latest material," the statement said.
Babies increasingly victimized
Europol's Georges said the victims varied in age but that there was a grim and growing trend of sexual abuse of babies under 18 months of age.
She added that the investigation was continuing and that more arrests were expected.
Steven Wilson, the head of Europol's EC3 cybercrime center, said pursuing people connected to child sexual abuse and exploitation material is a "key part" of Europol's work.
"We know that individuals are abusing online platforms and networks to distribute child sexual abuse material and are determined to target them and bring them to justice," Wilson said.
Arrests were made in all European Union countries except for the Czech Republic and Malta, but Europol did not give a breakdown of the arrests by country, although according to the Italian statement, at least five were arrested in Italy.
Last year Europol reported that criminals were increasingly selling live streams of child sex over legitimate chat sites and apps such as Skype in exchange for hard-to-trace virtual currencies like Bitcoin.
In one of the largest busts of its kind, Europol coordinated a sweep in 2011 after identifying 670 suspects - the result was 184 arrests.
bik/sms (AFP, dpa)