ASX telco shares are holding up fairly well in the wake of the massive Optus data breach.

News of the Optus hack, which may affect as many as 9.8 million customers, broke yesterday when the ASX was closed for the national holiday honouring the Queen.

We'll look at the key details below.

But first…

How are ASX telco shares faring following the Optus hack?

ASX telco shares are trading largely in line with the benchmark today.

In early afternoon trading the S&P/ASX 200 Index (ASX: XJO) is down 1.9%, following on from Wednesday's 0.75% rate hike from the United States Fed and some decidedly hawkish words from Fed chair Jerome Powell.

Meanwhile, the Telstra Corporation Ltd (ASX: TLS) share price is down 1.4% to $3.79 per share. And rival telecom TPG Telecom Ltd (ASX: TPG) is down 2.1% to $4.87 per share.

Optus, as you likely know, isn't listed on the ASX. The company is 100% owned by Singapore's telco giant Singtel.

What data did the hackers steal?

Optus is currently working with Federal authorities and therefore has yet to divulge many of the details about the hack. Details which the company is still working to unravel itself.

What is known is that the cyberattack may have compromised customer data including names, birth dates, email addresses, phone numbers, and possibly passport and driver's license details.

As the Australian Financial Review reported, Optus said payment details and account passwords had not been compromised.

The breach has hit as many as 9.8 million current and former customers.

Optus CEO Kelly Bayer Rosmarin said, "We're also very confident that the 9.8 million is an absolute upper bound number".

Explaining why former customers may have had their data breached as well, Bayer Rosmarin added:

The reason that we hold on to customer data for a period of time is that that is the law. We have to be able to go back in our records for six years, and so we do hold information for the required length of time.

Addressing the media, Bayer Rosmarin was visibly moved, telling customers, "I'm very sorry and apologetic. It shouldn't have happened."

While Optus customers are urged to be extra alert to scams over the coming weeks, the news doesn't look to have had a material impact on the big ASX telcos.

The post Here's how ASX telco shares are faring following Optus hack appeared first on The Motley Fool Australia.