Police believe the suspects stole details of more than 10 000 online bank accounts and 10 000 credit cards. The suspects allegedly used those details to take over bank accounts containing some £1.14m, and to get away with £358,000.
"The total amount stolen using compromised credit cards has yet to be established, but by using the industry agreed standard formula is estimated to be worth more than £3m," the Met said.
Five men and one woman, aged 25 to 40, were arrested on suspicion of conspiracy to commit online banking fraud and Computer Misuse Act offences. The arrests took place on Tuesday 3 and Wednesday 4 August 2010 in London and Navan, County Meath, Ireland.
The arrests are part of Operation Dynamophone, a PCeU investigation into a network of suspects believed to have systematically obtained large quantities of personal information, such as online bank account passwords and credit card numbers.
The network is suspected of using online phishing in order to steal money from those accounts and use credit card details fraudulently. The offences have been committed almost entirely online, the Met said.
Police believe the gang sent large quantities of spam emails that directed victims to spoof websites that looked like legitimate online banking sites.
Once victims reached the site, they were lured into providing their banking passwords and other personal information. The suspects used this information to then enter the victims' online bank accounts and transfer funds unlawfully. Credit card details were obtained and exploited in the same way, the Met said.
The PCeU's Detective Inspector Colin Wetherill said the arrests had shut down the gang. "A great deal of personal information was compromised and cleverly exploited for substantial profit. By disrupting the operation we have hopefully prevented further loss to individuals and institutions across the UK," he said.
He urged the public to be careful when supplying their personal details online and referred people to the advice given at Getsafeonline.
Officers from the Met's Territorial Support Group and the Irish Garda Síochána Fraud Investigation Bureau helped with the arrests. The suspects are being held at a central London police station. Police inquiries are ongoing, the Met said.
The PCeU's future is presently in limbo while the government reorganises the country's 43 police forces and a number of national services, including the Serious Organised Crime Agency.
This story was first published by Computer Weekly