Four people have been arrested in Spain though to be alleged "hacktivists" from the Anonymous group.
The information was reported by the European Police Office Europol.
Europol had coordinated the joint operation with the Spanish police.
The operation, codenamed Thunder, was the result of an 8-month-long investigation against a group of hackers, believed to be responsible for attacks on sites and servers and for releasing on the internet personal data of Spanish police officers.
According to an article of Public Service Europe, one of the suspects arrested, nicknamed "Thunder", was allegedly responsible for the administration of some of the secure communication channels used by Anonymous.
The servers used for this purpose were hosted by companies located in the Czech Republic and Bulgaria, although they were remotely controlled from Spain, Europol says.
Once the links with other member states were discovered, investigators from the Spanish National Police cybercrime unit contacted the Europol cybercrime center in order to coordinate the actions.
An Europol spokesman is quoted saying: "Immediately, after the first contact from the Spanish police authorities, Europol acted as a hub of information; facilitating the exchange of communications among the police investigators assigned to this case in their respective countries. This direct and quick response allowed in a very short period of time, the retention of the data contained in the servers hosted in Bulgaria and Czech Republic. Once the judicial authorities in these countries had approved the seizure of the servers, experts from Europol were deployed to Bulgaria and to Spain to provide on-the-spot support with the simultaneous arrests, house searches and disruption of the servers."