THE collapse of IT systems at Ulster Bank offers us a vivid illustration of how vulnerable we become when computers say no.
For the past seven days thousands of people up and down the country have had trouble with their bank accounts after a reported software update at parent company RBS went wrong and caused Ulster banks' IT systems to break down.
For many, bills have gone unpaid, holidays have had to be abandoned and pay day has yet to come.
The situation has echoes of the moment in the Hollywood thriller Die Hard 4 when Bruce Willis's ageing detective John McClane discovers just how much havoc can be wrought through a computer keyboard.
Hackers have infiltrated America's IT systems and brought the country to its knees, taking down the transport grid, crippling its banking sector and knocking out utilities such as water and electricity.
It is left up to a more informed younger colleague to explain what has happened. "They call it a fire sale," he says. "Because everything must go."
The film is Hollywood at its most paranoid. But it taps into our legitimate concerns that the world's reliance on computers leaves us vulnerable when they go wrong or are attacked. Computers make the world go round.
But like any piece of machinery, sometimes they break down. As Ulster Bank and their parent RBS have discovered.
Yesterday, RBS group chief executive Stephen Hester promised customers that the banks had "turned a corner" in dealing with the defective systems and said senior executives would face "proper accountability" for the fiasco.
An email sent to account holders added that the banks would waive overdraft fees for those caught up in the payments backlog. But Mr Hester was faced calls to be stripped of his bonus for a second year.
Sadly RBS is not the only banking group within the global financial sector to have been hit by computer glitches. In the past two years, HSBC, JP Morgan and TD Bank have had to navigate their way through angry consumer backlashes after their IT systems suffered glitches. Earlier this month, just half an hour of computer troubles on the American stock exchange racked up a $40m bill for Nasdaq, which had to reimburse investors who tried to by Facebook shares but couldn't.
"Taken on an individual basis these glitches seem like small fry," said one IT expert within the banking sector, who asked not to be named. "When you add them up, though, you have to start asking yourself whether we're really doing enough to make sure we are prepared for the worst case scenarios."
But banking is one sector among thousands that need computers to work properly.
"Ultimately, when you look around there's barely an industry or system that doesn't rely on computer technology to run some of its core functions," says Rik Ferguson, a cyber-security analyst at Trend Micro.
Cyber security is often portrayed as protecting an organisation from outside attack.
The threat of hackers and those who want to break in to steal data, money or just create carnage is real. But while companies spend millions building walls to keep people out, they often fail to make sure the houses inside are constructed properly.
Jay Sappidi, senior director at CAST Research Labs, which specialises in testing the quality of software coding, the building blocks of IT programmes, said: "It's like building a house. You create a building which has a bedroom, a kitchen and a bathroom. Everything appears to be working fine. But what you haven't done is tested whether it can withstand a rainstorm or an earthquake."
Ulster Bank/RBS's current software woes do not appear to have been caused by an external threat.
Official company statements have so far blamed unspecified "technical glitches". But insiders say the problems began when a software update went wrong.
Critics -- including the Unite union and IT experts -- have accused the bank of compromising its computer systems by outsourcing key work to India.
RBS has insisted the software glitch was a local problem, which rules out outsourcing but does little to defend the company from the accusation that its coding was not up to scratch.
Cyber space is often thought of as an entirely ephemeral thing.
But while data is pinged around the world wirelessly the internet itself still relies on physical structures such as servers and cables. And like any physical structure, it can be damaged.