Millions of Optus customers were on Wednesday affected by a nationwide network outage that impacted mobile, internet, and landline services.
The network dropped out about 4am on Wednesday, with customers unable to make or receive calls, or connect to the internet.
Here's everything you need to know.
What caused the Optus outage?
Optus chief executive Kelly Bayer Rosmarin revealed on Wednesday afternoon that a "technical network fault" caused the outage, but did not provide further details.
"Until we've done a full thorough root cause analysis, we really can't provide more information," she told ABC News.
"What I can say is that it was a technical network issue, and that our teams have worked very, very hard to get services restored as quickly as they possibly could."
Bayer Rosmarin also reiterated that outages like Optus experienced on Wednesday were "a very rare occurrence".
"When you operate a critical infrastructure that's 24/7, you do everything you can to plan to have that available 100 per cent of the time, and most days you succeed."
"Unfortunately, today was not one of those days, and we will investigate that thoroughly and understand what we can learn from it."
How bad was the Optus outage and who did it affect?
The outage impacted more than 10 million Optus customers in Australia, and overseas.
Coles Mobile, which uses the Optus network, confirmed on its website that it was also experiencing a service outage.
Some small businesses were forced to turn away customers because their EFTPOS machines, phones, and network systems were all impacted, while Melbourne train services were also interrupted early on Wednesday.
Commonwealth Bank confirmed its call centres were unable to receive incoming calls due to the outage, but that its ATMs, internet banking, app, branches and other services were still available.
It said customers could still contact it via the app or online banking but said there could be delays.
Several hospitals and healthcare services across the country also reported issues with their phone lines, with some urging patients to contact them via email instead.
While most Optus mobile customers were still able to call triple-zero, those with landlines could not.
"If Optus customers need to call emergency services, we suggest finding a family member or neighbour with an alternative device," the telco said on X.
Fire Rescue Victoria said due to the outage, some external calls to its phone numbers were being impacted.
The impact of the outage on state and federal government agencies, such as Medicare, was "being monitored", Rowland said.
Workforce Australia confirmed mutual obligations for Wednesday .
When was the Optus outage fixed?
Optus confirmed late on Wednesday afternoon that its services had been restored, more than 13 hours after the outage began.
"Customers should now be able to be back online," an Optus spokesperson said in a statement.
"We know that customers rely on our services, which is why the whole team at Optus has been working hard to fix this.
"We again thank customers for their patience."
Earlier, Bayer Rosmarin said Optus was "working to restore services for our customers as a priority", but didn't indicate how long that could take.
"The team has tried a number of paths of restoration," she said.
"So far, we have not had the result we have hoped for and we're pursuing every avenue to get everybody back online as soon as possible.
"When we have an identified root cause and a time for restoration, we'll be updating everybody."
Optus CEO Kelly Bayer Rosmarin. Source: AAP / Supplied/PR Image
Will Optus customers be able to get compensation?
Bayer Rosmarin said Optus was considering the ways it could thank its customers for their patience and rewarding them "for their loyalty".
"We'll definitely consider every avenue as we turn our attention now that services are restored to how we work with our customers to make sure that they know how much we care about our customers and how hard we're working to give them this reliable, great service," she said.
Earlier, Federal Communications Minister Michelle Rowland said it was "probably too early" to be discussing compensation or other consumer rights.
"But I do reiterate the statement of the TIO (Telecommunications Industry Ombudsman) that it is important, especially for small businesses, to keep receipts, so that any recourse and any redress that may be available to them has that evidentiary base."
