Optus claims “changes to routing information” after a “routine software upgrade” were to blame for last week’s national outage, affecting 10.2 million Australians and impacting 400,000 businesses.

In a statement released Monday afternoon, Optus said its network was affected by “changes in the routing of information from an international peering network” at around 4:05 a.m. AEDT last Wednesday, “following an upgrade routine software”.

“These routing information changes propagated through multiple layers of our network and exceeded predefined security levels on key routers that could not handle them,” the company said.

“This led to these routers disconnecting from the Optus IP Core network to protect themselves.”

The scale of the outage forced Optus technicians to physically reconnect or reboot the system, the operator said, and also meant that investigating the cause “took longer than we would have.” wish”.

“The restoration required a large-scale effort by the team and, in some cases, required Optus to physically reconnect or reboot routers, requiring people to be dispatched to a number of sites in Australia,” said an Optus spokesperson.

“This is why the restoration was gradual during the afternoon.

“Given the widespread impact of the outage, investigations into the issue took longer than we would have liked as we considered several different paths to restoration.

“Restoring the grid has always been our priority and we then established this cause in collaboration with our partners.”

Optus says it has since made changes to its network to resolve the issue so that it does not occur again, and that it will “continue to invest” to improve the resilience and services of its network.

It comes after Optus made an extra 200GB of data available to its customers from Monday to compensate for last Wednesday’s outage.

Optus faces a number of inquiries and inquiries following the outage, including a Senate inquiry which will hold its first public hearings on Friday.

Kelly Bayer Rosmarin, CEO of Optus, is currently the only confirmed witness.

The telecommunications company said in a statement that it supported and “fully cooperated” with reviews by the government and the Senate.