BBC New writes authorities across Europe worked together to shut down Ramnit, a botnet that had over three million PCs under its command. Ramnit spread malware via phishing e-mails and social networking websites like Facebook to infect computers and give criminals access to sensitive personal information like passwords and banking data.
An NCA spokesman said that Ramnit had spread the malware via seemingly trustworthy links sent out on phishing emails or social-networking websites.
He said: "If users running Windows operating systems clicked on the links, the malware would be installed, infecting the computer.
"Infected computers would then be under the control of criminals, enabling them to access personal or banking information, steal passwords and disable antivirus protection."
The agency's National Cyber Crime Unit (NCCU) worked with the authorities in the Netherlands, Italy and Germany, in an effort coordinated through Europol's European Cybercrime Centre, to target the command-and-control servers used to run the scheme.