And this was plainly apparent to millions of Germans trying to spend their own money this week, as banks there estimate that around a third of the country's debit and credit cards stopped working.

And since Germany is a nation of debit card users, the problem really hit home on Monday of this week, when people started returning to work and resuming their normal lives after the holiday break.

Germany bankers are still working out what happened, but it appears that, due to a lack of base conversion, central banking software treated 10 as a hexadecimal value, instead of a decimal one. In hexadecimal, 10 is 16, meaning the date appeared as 2016.

And since most debit and credit cards rarely span more than five years, many Germans found their cards being treated as expired when trying to spend their money or draw cash.

The AFP newswire reports that mostly cards with smart chips in them have been affected. The German Savings Bank Association, the DSGV, has said that over 20 million of its electronic cash cards and 3.5 regular cards had been affected.

Other German banking associations such as BDB and BVR also admitted having issues with many of their estimated 6.5 million cards.

Anecdotal evidence suggests that most Visa/MasterCard cards, as well as their Maestro and other card subsets, were not affected by the problem, but German EC smart cards were hit badly, as they use a central authorisation and clearing process.

German banks say that they expect to resolve the problems by next Monday and are working around the clock to reconfigure their computers. In the meantime, cardholders are being advised to carry cash as well as their cards with them.