The messaging service called MATRIX was discovered on the phone of a criminal convicted for the murder of Dutch celebrity crime reporter Peter R. de Vries in 2021, Europol said.

A large-scale investigation by the Dutch and French authorities intercepted the messaging service and monitored activity for three months, deciphering more than 2.3 million messages in 33 languages.

"The messages that were intercepted are linked to serious crimes such as international drug trafficking, arms trafficking, and money laundering," Europol said.

"Authorities were able to monitor the messages from possible criminals, which will now be used to support other investigations."

Europol said the main servers in France and Germany were taken down, and one suspect was arrested in France and two in Spain. Homes were also searched in Lithuania.