Complaints about the tax office are down by almost a third as it learns the lessons of an unprecedented outage of its online services in 2016-17.
A parliamentary committee is following up an auditor-general report which found the Australian Taxation Office failed to properly grasp system failure risks when its online services went down in late 2016 and early 2017.
The outages were heavily criticised at the time by regular users such as tax agents and small businesses, but the ATO insisted no data was compromised.
ATO chief information officer Ramez Katf on Friday told the committee in Canberra a dodgy computer cable on a system which was less than a year old was to blame for the failure.
But work was well under way on a major refresh of the hardware and software and in the way in which the ATO worked with clients.
Mr Katf said the ATO has in the past tax year received 11.6 million electronically submitted tax returns, with 3.5 million coming through apps.
In 75 per cent of cases, refunds had been processed in less than five days.
"Our complaints are down 30 per cent," he said.
"We have now recalibrated our capability and are performing better than we have ever done."
