A communications platform used by the Department of Defence has been hit by a ransomware attack.
Hackers targeted the ForceNet service, which is run by an external provider and used by public servants and military personnel.
Government officials said no data of serving or former military personnel appeared to have been compromised or stolen.
In an email to all staff, the defence secretary said the matter was being taken "very seriously".
The attack happened earlier this month.
Assistant Defence Minister Matt Thistlethwaite said the department was being prudent by notifying all personnel despite no information being stolen.
Defence has suggested its staff change their passwords and use two factor authentication.
"I want to stress this isn't an attack or breach on defence ICT systems," Mr Thistlethwaite told ABC radio.
"It's on an external provider defence contracts to run one of their websites."
Cyber support has been offered to military personnel who believe they may be affected.
Defence is partnering with an identity and cyber support company called IDCARE to protect staff.
The department has been contacted for comment.
