A network apparently using WhatsApp to distribute images of child sexual exploitation has been disrupted by dozens of arrests, according to police.
A total of 39 suspects were apprehended in Europe and South America, following action by the Spanish National Police, Europol and Interpol.
Spanish investigators discovered dark web sites directing users to private WhatsApp groups last year.
Researchers then verified these groups were used to share illegal images.
House searches conducted during the arrests had led to the seizure of "hundreds of devices containing several terabytes of child sexual exploitation material", according to Europol.
Spanish police have added that this included more than 360,000 files.
Operation Tantalio involved co-ordinated action in Germany, Spain and Portugal as well as several South American countries including Argentina, Chile and Ecuador.
Interpol has said that "hundreds" of the images and videos discovered have been entered into its international child sexual exploitation (ICSE) database.
It allows investigators to compare such material and make connections between victims, abusers and locations by "analysing the digital, visual and audio content".
Efforts are now being made by police to identify any child victims.
"These offenders are pushing the boundaries of modern technologies to try to avoid being caught by law enforcement," said Rob Wainwright, director of Europol.
"This case is an excellent example of global law enforcement cooperation, led by the Spanish National Police.
"We need to continue to combine our joint resources and skills to tackle this threat to our children and bring these offenders to justice."
A spokesperson for WhatsApp, which is owned by Facebook, said: "Child exploitation has no place on WhatsApp.
"When we're made aware of these accounts, we investigate, disable users that violate our terms, and assist with law enforcement as they track down and prosecute criminals."