Spanish police have arrested 34 people in a nationwide operation against an international crime ring known as “Black Axe” on accusations of fraud, money laundering and document forgery, Europol said on Friday.

Black Axe originated in Nigeria as a student confraternity in the late 1970s and has since evolved into a structured, violent criminal organisation dealing mainly in cyber-enabled financial crime, Reuters reported.

The arrests were carried out across several Spanish provinces from Seville in the south to Barcelona in the northeast with support from Europol, the European Union Agency for Law Enforcement Cooperation.

Europol said the operation was coordinated with authorities in Germany as part of a wider investigation.

The organised crime network allegedly recruited money mules in impoverished areas of Spain with high unemployment rates.

“Most of these vulnerable individuals are Spanish nationals and are exploited to facilitate the network’s criminal activities,” Europol said in a statement.

Investigators estimate that the network had defrauded its victims of more than 5.9 million euros ($6.87 million).