What caused the massive nationwide Telstra outage

Telstra’s nationwide outage was caused by software bug that led to a timing server issue  before disconnecting customers across the country and preventing more than 300 people connecting to Triple Zero.
Customers from around Australia were reporting issues with Telstra and other related companies that use the Telstra service, including Boost, Belong and Aldi.
The troubles began at about 5:00 am with customers from Sydney, Melbourne, Brisbane, Perth, Canberra, and Adelaide lodging comp