Police said today the men are accused of using a specially outfitted computer inside a Santander bank branch to seize control of the bank's computer systems.
The 12 suspects range in age from 23 to 50. Police said they had prevented a "multi-million pound" loss from the Santander branch at the Surrey Quays shopping center.
Police said it is not yet not clear if any money was taken from the bank before the arrests were made. Searches were being carried out in six different locations in the greater London area.