Yesterday, up to 100,000 customers of Ulster Bank on both sides of the Border, and many times that number of customers at its UK parent bank RBS, found their accounts suddenly "frozen", leaving them unable to carry out transactions online or check their balances at their branches.
In an age when most of us do at least some of our banking electronically, an IT glitch such as that experienced by RBS can have extremely serious consequences for its customers.
Payments aren't made into customers' accounts and they in turn are unable to make payments to other accounts.
Standing orders, bills and other regular payments are at risk of going unpaid and customers find themselves with unexpected, and all too often unauthorised, overdrafts.
Ever since the first ATM machines made their debut in this country, the banks have been desperately trying to persuade the public to do more of our banking electronically.
They have made it increasingly difficult and expensive for us to conduct our business with a real-live human being in a branch.
The banks justified this move to electronic banking on the grounds that it was cheaper and more efficient.
While we will have to take the banks' word for it that electronic, including on-line, banking is cheaper, yesterday's events make it harder to believe that it is more efficient.
If the banks want us to do our business with them electronically then we as customers have a right to expect that their IT systems will work properly.
Yesterday's events will have done nothing to enhance consumer confidence in electronic banking.