Dridex malware, also known as Bugat and Cridex, has been developed by technically skilled cyber criminals in Eastern Europe to harvest online banking details, which are then exploited to steal money from individuals and businesses around the world.

Global financial institutions and a variety of different payment systems have been particularly targeted, with UK losses estimated at £20m.

Some members of the public may also have unwittingly become victims of the Dridex malware and the NCA is encouraging all internet users to ensure they have up to date operating systems and anti-virus software installed on their machines, to protect themselves from further cyber crime attacks.

Computers become infected with Dridex malware when users receive and open documents in seemingly legitimate emails.

The NCA assessed there could be thousands of infected computers in the UK, the majority being Windows users.

Users are urged to visit the CyberStreetWise and GetSafeOnline websites where a number of anti-virus tools are available to download to help clean up infected machines and get advice and guidance on how to protect themselves in the future.

The NCA is conducting activity to “sinkhole” the malware, stopping infected computers – known as a botnet – from communicating with the cyber criminals controlling them.

This activity is in conjunction with a US sinkhole, currently being undertaken by the FBI.

The agency’s National Cyber Crime Unit (NCCU) has rendered a large portion of the botnet harmless and is now initiating remediation activity to safeguard victims.

The FBI and the National Crime Agency, with support from EC3 and JCAT at Europol, the Metropolitan Police Service, GCHQ, CERT-UK, the BKA in Germany, the Moldovan authorities and private sector security partners are attempting to frustrate the criminal networks.

According to the NCA this has resulted in a significant arrest, with more expected, and worldwide disruption of a sophisticated cyber criminal network.

Mike Hulett, head of operations at the National Crime Agency’s National Cyber Crime Unit said: “This is a particularly virulent form of malware and we have been working with our international law enforcement partners, as well as key partners from industry, to mitigate the damage it causes. Our investigation is ongoing and we expect further arrests to made.

Executive assistant director Robert Anderson from the FBI said: “Those who commit cyber crime are very often highly-skilled and can be operating from different countries and continents.

“They can and will deploy new malware and we, along with our partners, are alive to this threat and are constantly devising new approaches to tackle cyber crime.

“We urge all internet users to take action and update your operating system. Ensure you have up to date security software and think twice before clicking on links or attachments in unsolicited emails”.