Cybercriminals have stolen almost 100 staff logins from Australia’s “Big Four” banks, potentially exposing these financial institutions to serious cyber threats including data theft and ransomware attacks, according to recent findings from cyber intelligence firm Hudson Rock.
The compromised credentials belong to current and former employees and contractors at ANZ, Commonwealth Bank, NAB, and Westpac, with ANZ and Commonwealth Bank experiencing the highest number of breaches. All stolen credentials included corporate email addresses with access to official bank domains.
“There are around 100 compromised employees that are related to those four banks,” said Hudson Rock analyst Leonid Rozenberg. While this number is significantly smaller than the 31,000 customer banking passwords recently reported stolen, the security implications could be more severe.
“Technically, [attackers] need only one [login] to do a lot of damage,” Rozenberg warned.
The credentials were stolen between 2021 and April 2025 using specialized “infostealer” malware designed to harvest sensitive data from infected devices. These stolen credentials have subsequently appeared on Telegram and dark web marketplaces.
Security experts explain that these breaches could potentially give hackers “initial access” to the banks’ corporate networks. While banks employ additional security measures such as Multi-Factor Authentication (MFA), specialized cybercriminals known as “initial access brokers” focus on finding ways around these protections, often targeting employees working from home.
The investigation also uncovered a concerning number of compromised third-party service credentials connected to these banks, with ANZ having more than 100 such breaches and NAB more than 70. These compromised services could include critical communication and project management tools like Slack, JIRA, and Salesforce.
All four banks have responded by stating they have multiple safeguards in place to prevent unauthorized access. NAB reports actively scanning cybercrime forums to monitor threats, while CommBank noted investing over $800 million in cybersecurity and financial crime prevention last financial year.
The Australian Signals Directorate has already warned that infostealer infections have led to successful attacks on Australian businesses, highlighting that this threat extends beyond the banking sector to organizations across all industries.