Optus CEO Kelly Bayer Rosmarin reveals the reason why she said NOTHING for hours about worst outage in Australian history as she faces Senate grilling

Embattled Optus CEO Kelly Bayer Rosmarin has explained why it took her seven hours to front up to customers during the telco's nationwide outage which left more than 10 million Australians cut off from phone and internet services.

Ms Bayer Rosmarin was called upon to front up to a Senate inquiry about what went wrong on Wednesday November 8, when customers around Australia woke up to no service.

Communications Minister Michelle Rowland was fielding calls from journalists from about 5am, and fronted up to a press conference early on in an attempt to ease public concern.

But the Optus CEO herself didn't speak publicly on the crisis for several more hours, calling ABC Radio via WhatsApp shortly after 10.30am for a short interview about the matter.

She faced intense backlash for appearing to go missing during those crucial early hours, but now has told the inquiry she had good reason for the decision.

'I wanted to ensure before I spoke that we could at least rule out the possibility of malicious activity,' she said.

'As soon as our cyber specialists ruled this out, I began publicly fronting the issue on behalf of my team.'

Ms Bayer Rosmarin said the decision was two-fold - she was also working closely with her team to make decisions about the call centres, which had also crashed, and whether or not it was wise to open physical stores during the outage.

Greens Senator Sarah Hanson-Young, who is the chair of the committee overseeing the Optus inquiry, said customers had a right to know if they could continue to have confidence in the operator. 

The 12-hour outage last Wednesday affected Optus' entire telephone and internet network and prevented some calls to emergency numbers.

It was the second major crisis for the telco in the last 12 months after a cybersecurity breach compromised the personal data of customers.

Ahead of the Senate hearing, the Australian Financial Review reported Ms Bayer Rosmarin was considering her position.

The chief executive, who has held the top job at Optus since April 2020, could depart as soon as early next week, the publication said.

Asked if Ms Bayer Rosmarin should resign, Senator Hanson-Young said it was a question for the board and the chief executive.

'But I must say I think this has been handled atrociously. It's not the first time under this leadership that Optus has not been able to front up to the customers and tell the public what's going on,' she said.

Optus has blamed the outage on a routine software upgrade, when changes to routing information cascaded through multiple levels of the telcos network.

Speaking at the inquiry, Ms Bayer Rosmarin said: 'The reality is that our network should have coped with this change, but on this occasion it did not.

'We effectively performed a hard reboot of the network - this commenced at about 10.30am with the vast majority of customers recovered by 2pm and 99 per cent by 4pm.

'The actions we took were a brute force resuscitation of the network. We had not yet identified the cause of the issue, and so whilst the crisis was over for our customers by 4pm, it was not over for our teams, who needed to immediately shift focus to what had happened to the network to ensure it would not happen again.

This work continued for many days... I would like to acknowledge and thank the team for their tireless recovery efforts under enormous pressure.'

The CEO said she 'wholeheartedly believes' she and her team did everything they could to 'provide timely, accurate and credible information' but accepts there is always more that could be done.

'There is no question the outage itself initially adversely affected our ability to more effectively communicate with each other, our consumers, media and government in the early hours of Wednesday morning.'

Ms Bayer Rosmarin revealed she did not speak to the relevant minister - Ms Rowland - until 8.30am, about four hours after the outage started.

At that time, she had no reason to believe that Triple-zero calls were not going through, as the network is designed to reroute emergency calls through other networks in the case of an outage.