Hacking group Anonymous on Friday claimed to have shut down a computer server belonging to Australia's domestic spy agency ASIO, reportedly briefly closing down access to its public webpage.
The Australian Security Intelligence Organisation (ASIO) acknowledged some disruption to its website.
"ASIO is aware that there may have been some technical issues with its public website," a spokesperson said.
"ASIO's public website does not host any classified information and any disruption would not represent a risk to ASIO's business."
Micro-blogging site Twitter has carried comments in recent days that ASIO and Defence Signals Directorate (DSD) sites were being targeted by Australian hackers linked to Anonymous.
In an early Thursday morning post on its Twitter feed Anonymous Australia (@AuAnon) wrote: "The anonymous Operation Australia hackers have today again been busy with further attacks on the ASIO and DSD website."
The Sydney Morning Herald reported that ASIO's website was down for at least 30 minutes Friday morning, but it appeared to be loading normally Friday afternoon.
Operation Australia, which has its own @Op_Australia Twitter stream said it would "stop the attacks at 10pm Aus. BUT we will never stop watching!".
The personal and departmental websites of Attorney-General Nicola Roxon, the ruling Labor party's South Australia branch and Tasmania police sites were also targeted in the plot, which was referred to as #TangoDown.
It appeared linked to a controversial government plan to store the web history of all Australians for up to two years which was shelved Thursday until after the 2013 elections.
The group Anonymous, which is believed to be a loosely affiliated network of "hacktivists", has attacked sites around the world including those of MasterCard and Visa, the US Justice Department, and the Tunisian and Yemen governments.
In 2011, ASIO revealed it had established a cyber intelligence unit although it is believed to have been operating for some time before it was announced.
The then attorney-general Robert McClelland said while traditional espionage still posed risks, "the explosion of the cyber world has expanded infinitely the opportunities for the covert acquisition of information by both state and non-state actors."