The notorious hacking group Anonymous crippled a computer server at the domestic spy agency, the Australian Security Intelligence Organisation, and claimed the agency's website would be unavailable for the rest of the day.

An Australian arm of the loose-knit hacking group Anonymous announced its attack via its Twitter account shortly after 10am today. "Server http://www.asio.gov.au has been down for some time now, And will be for the rest of the day!" the account stated.

An image Anonymous Australia uses in a YouTube video explaining why it did the hack.

ASIO's website was down for at least half an hour this morning and now either works, loads slowly or doesn't work at all. The spy agency said in a statement that it was "aware that there may have been some technical issues" with its site, adding that it did "not host any classified information [on it] and any disruption would not represent a risk to ASIO's business".

Over the past week Anonymous' Australian Twitter account has been boasting it will attack the ASIO website and that of Defence Signals Directorate. "The anonymous Operation Australia hackers have today again been busy with further attacks on the ASIO and DSD website," Anonymous Australia wrote on Wednesday.