The Australian Taxation Office has restored its website and most of its online services after an outage.
A statement on the ATO's website just after 2pm AEST on Thursday said services were "progressively coming back online".
"Sorry for today's disruption," the ATO said.
The outage sparked anger across the country, during one of the busiest times of the year for book-keepers and accountants.
Labor frontbencher Ed Husic said the government had failed to fully explain past failures and needed to come clean on this one.
"Accountants have been left in the dark as to what's gone on and have been concerned about the impact that these shutdowns have had on their business," Mr Husic told AAP.
Last year the ATO suffered what tax commissioner Chris Jordan described as the "worst unplanned system outage in recent memory".
It was caused by an unprecedented failure of storage hardware, which had been upgraded in November 2015 by Hewlett Packard Enterprise.
What compounded the problem was the subsequent failure of the ATO's back-up arrangements.
In February, Mr Jordan was scathing of media coverage which suggested tax time 2017 was under threat.
In May, Mr Jordan told a Senate estimates hearing the IT systems at the ATO had been fully restored after the failures of late 2016 and earlier this year.
"We've already rebuilt our storage system to the latest in world-class standards, replacing the faulty equipment with new technology," Mr Jordan said.
The ATO collects more than $440 billion in tax revenue each year through its electronic lodgement system.
