A severe system outage that knocked out internet banking and delayed routine payment processing dragged late into a second night overnight for National Australia Bank.NAB at one point yesterday afternoon advised customers on social media that it resolved the system failures, in a message posted 18 hours after the bank first acknowledged the issue amid the first wave of discontent on Twitter.Its UBank Twitter feed stated: "Our services have now been restored and we thank you for your patience."A continuation, or recurrence, of the strife produced a filmed apology by late afternoon from NAB's chief operating officer Andrew Hagger and assurances of diligent work to resolve the problem.Hagger did not outline the nature of the difficulty in the bank's engine rooms.The episode is cruelly timed, given the appearance at a sensitive political inquiry this morning of NAB's managing director, Andrew Thorburn.Yesterday evening NAB's social media shed no more insight beyond repetition of boilerplate apologies and the assurance "we're working to have the payments processed as soon as possible, but no ETA as of yet."This morning the bank's home page continued to inform customers "We've been experiencing outages to some of our services."The Twitter feed from last night airs the uncertainty on the resolution of the problem.Responding to the torrent NAB advised: "We are working to process payments - hopefully your payment is received on time", soon followed by "I'm unable to give an answer on what will happen tomorrow Matt, I'm really sorry."Clarification published Friday, October 7.