National Australia Bank has pinned a recent 24-hour outage on IBM.

Media investigations this week claim an outsourced IBM staffer deleted a production domain name system (DNS) zone.

The change meant that on October 4, NAB’s mobile banking, its UBank subsidiary, contact centre, some payments processing and corporate systems went down.

NAB has not provided an explanation for the outage, but tech news outlet iTNews says the downtime was triggered by human error.

In 2010, the bank allegedly outsourced responsibility for its mainframes, storage and hosting, desktop fleet management, printing, service desks and operating systems to IBM.

The reports say an IBM staffer attempted to make a routine change, but deleted a primary DNS zone instead.

Primary zones hold the original data for all domains in the zone, but can be edited or updated, with changes replicated on any servers that host secondary or stub versions.

iTNews says IBM moved fast enough to stop the changes replicating to every server in the DNS.

But it took some time for the changes to propagate through the wider DNS, causing delays in the services coming back online.

Neither NAB nor IBM have made official comment on the claims.