The UK is among 30 countries that contributed to the dismantling of a cloud-computing network used by cyber fraudsters to target one million users every week with malware-infected emails.

The operation was led by Europol, the FBI and German police and supported by 30 law enforcement partners, including the UK’s National Crime Agency (NCA).

Europol hosted a command post at its headquarters in The Hague. From there, representatives of the involved countries worked together with Europol’s European Cybercrime Centre (EC3) and Eurojust officials to ensure the success of such a large-scale operation.

The operation followed a four-year investigation by the German police into the fraud linked to Avalanche that affected victims in 180 countries and is estimated to have run to hundreds of millions of dollars.

In a single day of co-ordinated action, more than 830,000 malicious web domains were taken down and communications blocked between criminals and the computers they controlled.

Five people were arrested, 37 premises were searched and 39 servers were seized, while 221 servers were put offline through abuse notifications sent to the hosting providers.

The removal of criminal control provides victims, many of whom will not know their machine is infected, with an opportunity to scan, disinfect and protect their computer against further attack.

Rob Wainwright, Europol director, said Avalanche has been a highly significant operation involving international law enforcement, prosecutors and industry resources to tackle the global nature of cybercrime.