A thief installed a device to allow associates to hack the computers of High Street banks as part of an organised crime gang’s cyber-theft of £90,000.

Dean Outram, 34, of Clifford Gardens, Kensal Rise, entered a branch of Barclays Bank in Lewisham, south-east London, on July 17 last year and was able to unlawfully gain access to the bank’s computers from which £90,000 was stolen.

Barclays reported the matter to the police, who recovered a keyboard, video and mouse (KVM) device - a box that allows a user to control multiple terminals remotely from a single computer - which Outram had installed.

Less than two months later the 34-year-old got into the Surrey Quays branch of Santander in Rotherhithe, south-east London, where he fitted another KVM switch onto the bank’s computers in an effort to access customer’s accounts.

Officers raided a property in Hounslow, west London, and discovered associates freshly logged on to the KVM device and accessing bank accounts although no money had yet been stolen. Ten arrests were made and Outram was apprehended close to the Santander branch.

In the gang’s first cyber attack, conducted in April 2013 on the Barclays Bank branch in Swiss Cottage with a KVM device by an associate of Outram, the criminals made 128 transfers worth £1,252,490 to a network of mule accounts set up to launder the stolen cash.

The fact Outram admitted two counts of conspiracy to steal on December 18 2013 at Southwark Crown Court can only now be reported following Thursday’s conclusion of the trial of co-defendants.

Temporary Detective Constable Inspector Jason Tunn, from the Metropolitan Police’s Cyber Crime Unit, said: “These convictions are the culmination of a prolonged and highly complex investigation by Metropolitan Police Service detectives into an organised crime group that sought to target London’s banks and credit card companies in order to steal millions of pounds.

“The police investigation has been successful thanks to the fantastic support provided to us by industry partners and today’s convictions are testament to what can be achieved through joint working.

“The sheer volume and size of the investigation undertaken has been staggering and the MPS detectives and industry partners, including Barclays and Santander, should rightly be praised for their immense efforts in solving this case.”

Three defendants were convicted on Thursday and another 10, including Outram, had previously pleaded guilty to conspiracy charges, and will be sentenced later.

The co-defendents came from all over including Putney in south-west London, White City in west London, Gospel Oak in north London, South Kensington in south-west London, Abbots Langley in Hertfordshire, and Milton Keynes in Bedfordshire.