Telstra has paid $2.5m in fines for failing to list close to 50,000 people as private numbers to prevent them being listed in public phone directories.

All mobile and landline phone numbers in Australia are stored in the Integrated Public Number Database (IPND), which is managed by Telstra, Australia’s largest telecommunications company.

When telecommunications companies register new phone numbers with customer information, they are required to specify whether the phone number should be listed or unlisted.

If a number is unlisted it won’t appear in public directories, but can be accessed by law enforcement and national security agencies.

The Australian Communications and Media Authorities (Acma) fined Telstra $2.53m for what it said was “large-scale breaches of rules intended to protect the privacy and safety of customers”. Telstra failed to correctly upload nearly 50,000 customers’ choices to have their number unlisted in the database, meaning those numbers were publicly identifiable.

The authority also found Telstra failed to provide or update the data on the national database for customers of its subsidiary internet service provider, Belong, on 65,000 occasions.

Acma chair Nerida O’Loughlin said that could leave some of those people at risk in an emergency when Triple Zero needs to locate someone, or to issue emergency alerts in floods or bushfires.

“The provision of these critical services can be hampered and lives put in danger if data is missing, wrong or out of date,” she said. “It is alarming that Telstra could get this so wrong on such a large scale.”

The failure to register unlisted numbers could also lead to harm, she said.

“When people request a silent number it is often for very important privacy and safety reasons, and we know that the publication of their details can have serious consequences,” she said.

A spokesperson for Telstra said the company had not met its own high expectations of its responsibilities to protect privacy and safety of customers.

“We self-reported these issues to Acma and took steps to correct them. We accept the Acma findings and have paid the infringement notice.”

It is the second time Telstra has been found in breach of the obligations, with the first finding in 2019 after Telstra self-reported it to the authority.

Acma said the $2.53m penalty was the largest of its kind to be issued for such a breach.