Australian Prime Minister Scott Morrison said Monday that “a sophisticated state actor” was behind the hacks of parliament and the country’s political parties first reported February 8.

“Our cyber experts believe that a sophisticated state actor is responsible for this malicious activity,” The Register cited Morrison as saying.

“There are a limited number of countries but we have low confidence at being able to publicly state who we think it is,” the head of the Australian CyberSecurity Centre, Alastair MacGibbon, told the Australian Broadcasting Corporation.

“Powerful nation-states have the requisite technology and other resources to cover up their attacks and operate in stealth mode,” agreed High-TechBridge CEO Ilia Kolochenko. “In light of incomplete or blurred visibility across many governmental IT systems, networks where virtually no single machine is up2date, alongside shadow and legacy applications, and a global cybersecurity skills shortage – it is unfortunately not that complicated for cybercriminals to remain unnoticed.”

Kolochenko said, “The real problem is represented by intrusions and data breaches that have already occurred but are not yet discovered, and worse – will probably never be.”