A man posing as an engineer apparently attached a KVM switch to a computer in Santander's Surrey Quays branch in order to control the PC remotely. Police said that although the device was successfully installed, it was never made operational.
According to a bank spokesman, Santander was already aware that it was a likely target and had already been working with police for three or four months prior to the incident.
"This was a sophisticated plot that could have led to the loss of a very large amount of money from the bank, and is the most significant case of this kind that we have come across," Det. Insp. Mark Raymond said in a statement. "I would like to thank our partners from the industry who have provided valuable assistance throughout this investigation."
A Santander spokesman told the BBC, "Through this cooperation, Santander was aware of the possibility of the attack connected to the arrests. The attempt to fit the device to the computer in the Surrey Quays Branch was undertaken by a bogus maintenance engineer pretending to be from a third party. It failed and no money was ever at risk. No member of Santander staff was involved in this attempted fraud."