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
Parents and psychologists have warned of a technology addiction crisis, with one mother revealing how her son "simply stopped functioning".
Hamid Ali Jafari, whose father Ali Yawar Jafari, 82, was killed said he prayed every day that he would die so he could see his father again.
Sajid Javid has used his first major speech since his appointment as Home Secretary to offer an olive branch to police officers.