The plotters behind the attempted Santander bank theft exploited the "inherent trust" of staff as they strolled into the branch dressed as IT workers, an expert said.
Had they succeeded, the crooks could have stolen reams of customer data and potentially committed a multimillion-pound heist.
But security experts said their technique was relatively simple.
It involved the use of a keyboard video mouse - a feature commonly used by a company's IT team to administer servers and computers remotely.
Gavin Millard, of internet security firm Tripwire, said those behind the "incredibly simple" scam would have planned to manipulate technology built into the computer so they could access the machine from another location.
It looks like they pretended to be maintenance workers and used people's inherent trust to gain access to these devices and reconfigure them.
They would then have been able to access the system remotely so they could see what was happening within the bank itself.
The way that they most probably did this was by taking advantage of very standard tools that are in modern desktops.
More top news
Drug gangs are exploiting large numbers of children and pushing them onto the frontline of the UK’s class A drugs trade, ITV News reveals.
Paramedics were called to reports of an unresponsive baby girl on a bus in east London - she later died in hospital.
Transport for London is not happy that its branding has been used.