Western Australia-based Defence shipbuilder Austal has been the subject of a cyber security breach and extortion attempt.

The company announced to the stock exchange on Thursday night that its Australian data management system had been targeted by an “unknown offender”.

Some staff email addresses and mobile phone numbers were accessed, according to the statement which acknowledged that a “small number” of customers had been affected.

It said it appeared the offender tried to sell some of the stolen material online “and engage in extortion”.

“The company has not and will not respond to the extortion attempts,” it said.

The company, which builds patrol vessels and frigates for the Australian Navy, said there was “no evidence to date that information affecting national security has been stolen”.

But it indicated the hackers got access to – or stole – drawings and designs of its ships.

“Ship design drawings which may be distributed to customers and fabrication sub-contractors or suppliers are neither sensitive nor classified,” it said.

Austal has defence contracts with several other countries, including the US, but said the breach was limited to Australia.

“The data breach has had no impact on Austal’s ongoing operations,” it said.

“Austal’s business in the United States is unaffected by this issue as the computer systems are not linked.”

The Federal Police and Australian Cyber Security Centre are investigating.

In a statement, the Defence Department said it was aware of the breach but confirmed: “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 the defence industry, and the need for industry partners to put in place, and maintain, strong cyber defences.”

Austal joins a growing list of companies, government agencies and institutions being targeted by cyber criminals seeking to steal information or disrupt operations.

While it was unclear who was behind this latest attack, Duncan Lewis, the head of Australian Security Intelligence Organisation, recently highlighted the growing threat to Australia’s national interests of “espionage and foreign interference”.

According to its website, the Australian shipbuilder has designed and constructed more than 300 vessels for more than 100 operators in 54 countries.

These include the littoral combat ship for the US Navy and the high-speed support vessel for the Royal Navy of Oman.

Austal designs, constructs and maintains the Cape Class Patrol Boat program for Border Force and the Royal Australian Navy, as well as the Guardian Class Patrol Boat for the Commonwealth of Australia.

-ABC