The men, aged between 24 and 47, were arrested on Thursday and Friday morning on allegations of conspiracy to steal from Barclays and conspiracy to defraud British banks.
They are accused of a theft in April, when a man purporting to be an IT engineer arrived at a Barclays branch in north London saying he was there to fix the computers.
He then attached a keyboard, video and mouse (KVM) device with a 3G router to one of the computers, according to a statement from the Metropolitan Police.
Such devices are routinely used by people in business to work remotely on their office computer systems, but it allowed the gang to remotely transfer money into their bank accounts.
“Those responsible for this offence are significant players within a sophisticated and determined organised criminal network, who used considerable technical abilities and traditional criminal know-how to infiltrate and exploit secure banking systems,” said Detective Inspector Mark Raymond of the Central e-Crime Unit.
Barclays recovered “a significant amount” of the money stolen, police said, but the arrests are the first in the five-month investigation into the crime.
Officers searched a number of addresses across London and Essex, east of the capital, and seized cash, jewellery, drugs, “thousands of credit cards” and personal data, the statement said.
One central London premises searched was described by detectives as the “control” centre of the operation.
Police foiled a similar plot against Santander last week, arresting 12 men accused to trying to take control of a computer in a branch in London’s financial district. Four men were later charged with conspiracy to steal.