Defence shipbuilder Austal's Australian business has been hit with a data breach and extortion attempt but insists there is no evidence of theft of national security information.
Some staff email addresses and mobile phone numbers were accessed in the breach.
The attacker tried to sell certain materials on the internet and engage in extortion.
However Austal said the company does not intend to respond to such threats.
"There is no evidence to date to suggest that information affecting national security nor the commercial operations of the company have been stolen," Austal said.
The federal government has been alerted to the cyber security incident.
The Australian Cyber Security Centre and Australian Federal Police are providing the company with assistance and advice.
As investigations continue, the Department of Defence says no compromise of classified or sensitive information or technology has been identified so far.
"This incident reinforces the serious nature of the cyber security threat faced by defence industry, and the need for industry partners to put in place, and maintain, strong cyber defences," the government said.
"Defence and the ACSC have provided cyber security assistance to Austal and are working with Austal to assess and mitigate harm."
Austal makes defence vessels for several markets, including the United States. The company said its US business was unaffected by the breach.
However a small number of stakeholders potentially impacted by the breach have been informed, the company said.
