German shoppers hit by a "Year 2010" computer bug that bit 30 million bank cards fell back this week on a popular and proven means of payment -- cash.

Ines Klem, 45, for instance, said she would withdraw "between 20 to 50 euros (30-70 dollars) on a regular basis to be sure to have no more problems."

Klem had tried to buy food and found herself with a full basket and no way to pay for it after her bank card failed to work as normal, a problem that at one point hit roughly one-quarter of all German bank cards.

"Everyone was looking at me at the check-out," she said.

Paul Rohr, 85, added that his bank "immediately gave me another (card) to get cash with," while Kaiser supermarket manager Uwe Werner said: "To be safe, people are paying in cash, something they often do early in the month."

The problem stems from a series of computer chips unable to cope with the changeover to the year 2010, leaving millions of Germans starting the new year unable to withdraw cash or to pay with plastic in shops.

The situation has since improved at cash distributors, with bank staff reprogramming software to read the card's black magnetic strips, but that is a temporary and less secure solution, and shop payments are still subject to some glitches.

The German HDE retail trade association said flawed cards had posed problems for about 20 percent of one million retail point-of-sale terminals in the country.

Worst hit were holders of cards issued by Germany's dominant public-sector savings banks and cooperative banks, but clients at private lenders Postbank and Commerzbank clients also had problems.

"Sometimes cashiers get cards to work by wrapping them in plastic film before inserting them into the payment terminal," Klem noted, a practice discouraged Thursday by the German credit association ZKA which warned it could damage the card and cash machines.

The problem was a reminder of the feared "Y2K" bug of a decade ago that had governments, businesses and individuals expecting the worst at the turn of the millennium. In the end, everything went smoothly.

This time around, German banks hope to reprogramme the defective cards via automated teller machines to avoid the cost of replacing them, estimated at 250-300 million euros.

The French firm Gemalto, a major supplier of bank cards, said it and German clients were making a extensive joint effort to develop "a corrective process that avoids the replacement of the affected cards."

The savings and regional bank association DSGV has estimated meanwhile that the situation should be back to normal by Monday.

Germans trying to make purchases abroad have also experienced difficulties as Europe works towards a harmonised electronic payment system with the Single Euro Payments Area (SEPA), a network that covers 32 countries.

The Stuttgarter Zeitung newspaper quoted Claus Jousten, head of Western Union in Germany, as saying: "We have seen a marked increase in transactions" with clients who want cash for business or holiday trips.

Back in Berlin, "the situation is not extreme," said Kerstin Haertel at the Thalia bookstore chain before adding: "There are always problems with cards."

A central bank study found Germans prefer to pay in cash anyway, with almost 58 percent of all transactions handled that way, compared with about 30 percent for all bank cards combined.