Australian telco Optus confirmed that a routine software upgrade was the reason for a widespread 14-hour outage last week.

The outage, which impacted millions of Australians last Wednesday (November 8), occurred following changes to routing information from an international peering network after a routine software upgrade at 4:05am.

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It caused transport delays and payment problems, and cut hospital phone lines. In total, more than 10 million people were affected, plus thousands of businesses.

Optus initially blamed a "technical network fault" for the outage.

“These routing information changes propagated through multiple layers in our network and exceeded preset safety levels on key routers which could not handle these. This resulted in those routers disconnecting from the Optus IP Core network to protect themselves,” said an Optus spokesperson.

"The restoration required a large-scale effort of the team and in some cases required Optus to reconnect or reboot routers physically, requiring the dispatch of people across a number of sites in Australia. This is why restoration was progressive over the afternoon.”

Optus apologized to its customers in the wake of the outage, and has offered 200GB of free data for mobile and small business customers.

The company's CEO ruled out offering financial compensation. Customers and business owners have called the offer a "token gesture."

One user on X revealed that her cat had alerted her to the outage, when its automatic WiFi feeder didn't deliver the cat's meal.