The malfunctioning of hardware supplied by Hewlett Packard Enterprise dates back to the second weekend of December 2016.
On Thursday, the ATO put out a media release at 11am AEDT, stating: "The ATO is experiencing issues relating to the hardware faults that occurred in December.
"We are replacing the affected hardware, but this process will take some time. Unfortunately, these issues are impacting services including the Tax Agent, Business and BAS Portals, ATO online, the Australian Business Register (ABR), Standard Business Reporting (SBR), and Superannuation online services.
"No taxpayer information has been lost or compromised and all available resources are working to resolve this as a priority.
"We apologise for any inconvenience taxpayers have experienced."
A later release, issued at 4.30pm, said: "Unfortunately we are continuing to experience issues with the systems impacted by this morning’s outage. These systems will not be available today.
"We are working to resolve these issues as a priority, and will continue to keep the community informed of our progress."
At the time of the December problems, the ATO was said to be trying to recover about one petabyte of unspecified data that had been affected by the crash.
Last month, the ATO said that it had commissioned Price Waterhouse Coopers to undertake a review into the system outage. It said PWC was given the job because of its expertise with ICT storage that was at the centre of the incident.