The Australian bank blamed a "critical security change" for glitches to its Eftpos and ATM network over the weekend. The problems surfaced after the bank had shut down its NetBank online system for an eight-hour period overnight Saturday to introduce instantaneous credit card transaction updates and extend an online identity verification service to online retail purchases.

After NetBank was rebooted, customers found valid transactions being declined at the point-of-sale and limits enforced on ATM transactions.

On Monday morning, the bank posted an apologetic tweet on microblogging site Twitter: "Thanks for your patience yesterday, all issues have now been resolved & all ATMs & EFTPOS are working. Apologies again for any inconvenience."

The glitch was an embarrassment for CBA, which had issued a bullish press release, promoting the extension of its NetCode SMS security service to online shopping. The service, which sends a one-time password to a customer mobile or personal authentication token, has already been applied to funds transfer transactions over NetBank.

CBA's online woes come just four days after neighbouring bank ANZ suffered a four-hour Eftpos and ATM outage - it's second in as many months. Rival Westpac is also in the doldrums after a software patch cut the carrying capacity on the bank's online service to 25%, leaving many customers unable to log in to their accounts.