Nine reported that Westpac had confirmed the incident, but not provided an indication as to how many people were affected.

PayID is available under the New Payments Platform and allows anyone to transfer money using a mobile number or an email address. But on the downside, one can confirm the name of an account holder by using their mobile number or email address.

A confidential memo obtained by Nine provided details about the leak. "On 22 May 2019, Westpac noted that a high volume (600,000) of NPPA PayID lookups was made from seven compromised Westpac Live accounts. "[Around 98,000] of the lookups successfully resolved to a short name and this was displayed to the fraudster," it said.

The Commonwealth Bank was the first to begin offering PayID in February last year.

Contacted for comment, a Westpac spokesperson said: "Westpac can confirm we had detected misuse of the NPP’s PayID functionality and we took additional preventive actions which did not include a system shutdown.

"No customer bank account numbers were compromised as a result.

"Westpac Group takes the protection of customer data and privacy extremely seriously and we continually monitor our systems."