Telstra Group (ASX:TLS) executives told an Australian Senate hearing on Friday that the company received reminders in 2022 and again in January this year to implement a software update on its server, which could have prevented a recent outage of its Triple Zero service.

At the hearing into the disruption of voice and data services, Telstra CEO Vicki Brady blamed the outage on "an intentional design change that had previously been made to the equipment to fix an earlier fault."

The design change was not properly documented, which caused the GPS card to not operate as expected when the device was restarted, Brady said.

Gerard Tracey, another executive at the company, said the outage would not have occurred if Telstra were operating on more recent hardware.

"Last week, Telstra let Australians down. We let our customers down, we let the community down, and we fell short of what people rightly expect from us," Brady said in her opening remarks. "For this I am deeply sorry."

She added that the company's investigation into the matter is ongoing.

Telstra shares gained nearly 2% in recent Friday trade.