Telecommunications company Optus has blamed a "routine software upgrade" as the cause of a major outage in Australia last week.
The incident disconnected 10.2 million Australians and 400,000 businesses for up to 13 hours last week.
In a statement, Optus explained that the network was affected by "changes to routing information from an international peering network" after a "routine software upgrade".
Services went down at about 4.05am AEDT and were not fully restored until 5.35pm.
The telco, which admitted the investigation took longer than expected, stated that routers disconnected from its core network following the maintenance.
"These routing information changes propagated through multiple layers in our network and exceeded preset safety levels on key routers, which could not handle these," a spokesperson for the company said.
"This resulted in those routers disconnecting from the Optus IP Core network to protect themselves."
Wednesday’s blackout severely impacted public transport, hospitals, businesses and banks across the country, and even cut off people’s ability to contact emergency services.
Optus has offered 200GB of bonus data as compensation.
The Australian government has announced an inquiry into the outage.
Optus CEO Kelly Bayer Rosmarin is scheduled to face a grilling by the Senate on Thursday.
"We are committed to learning from what has occurred and continuing to work with our international vendors and partners to increase the resilience of our network," the spokesperson said.
"We will also support and fully cooperate with the reviews being undertaken by the government and the Senate."
Australia’s Greens spokeswoman for communications, Sarah Hanson-Young, will chair the inquiry.
"The people who have been ripped off and let down deserve better," Hanson-Young said in a statement announcing the investigation.
"The lives and livelihoods of millions were acutely disrupted on November 8; phones were dead, the internet down, banking broken, childcare centres closed, schools impacted."
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