The Australian Taxation Office (ATO) has announced that most of its systems are back up and running after an "unforeseen complexity" during a system restoration left its core platforms offline last week.
Currently, the ATO's Tax Agent, Business and BAS Agent Portals, ATO Online services, and Standard Business Reporting services are available, and its Superannuation online services are expected to be functioning by late Monday morning.
However, the ATO's Australian Business Register is still undergoing restoration, and the tax office expects the remainder of its services to become available throughout the day.
"Our clients may experience some slowness as further work is undertaken to improve the overall performance of our systems," the ATO said in a statement on Monday. "Our focus will now turn to building system resilience to best ensure the stability of our services to the community."
The ATO reported on Friday that it had suffered another setback to its systems restoration and as a result was not expecting service availability to its key applications before the weekend.
On Friday morning, the tax office said both ATO and Hewlett Packard Enterprise (HPE) technicians had worked through the night to restore its systems and online services; however, its online services were still not operational by the afternoon.
"While there has been significant progress on their restoration plan, the process is highly complex," the ATO said. "While everything is being done to restore our systems as quickly as possible, we cannot make services available to the community until the integrity of the system is confirmed."
HPE upgraded the ATO's hardware back in 2015, which is "basically the same" hardware used by other large clients of the IT giant.
The ATO's website, tax agent, and business portals initially crashed on December 12. The outage continued through to December 13, when the ATO first called in HPE to help it determine the underlying cause of the problem that the ATO said was encountered for the first time anywhere in the world.
Three days later, Commissioner of Taxation Chris Jordan announced an independent review into the "unprecedented failure" and called it the ATO's worst unplanned system outage in recent memory.
At the same time, the ATO claimed almost everything was back up and running, but did admit that "some" data corruption was experienced as a result of the incident, and noted it was in the process of having the data fully restored from a back-up.
On December 20 -- more than a week after the initial hardware failure -- the ATO said it was still experiencing reduced functionality across some of its systems.
"What compounded the problem beyond the initial failure was the subsequent failure of our back-up arrangements to work as planned," Jordan explained previously. "The failure of our back-up arrangements meant that restoration and resumption of data and services has been very complex and time-consuming."
The tax office's systems fell over again on February 2, 2017, with the outage affecting all of its online services, including the ato.gov.au website.
The ATO has also appointed PwC to conduct an independent review into the long-running incident. The tax office expected the consultancy firm's review to provide insight into what actually happened and why, and what needs to be done to ensure the same incident does not occur in the future.