Hackers flying the Operation Australia flag claim to have brought down multiple government websites over the weekend.

Tweeting from the @Op_Australia account, the hackers claimed to have brought down the websites belonging to the Australian Secret Intelligence Service (ASIS), the Australian Security Intelligence Organisation (ASIO), the Defence Signals Directorate (DSD), the Australian Federal Police (AFP), the prime minister, and federal Attorney-General Nicola Roxon.

Asio, Please fix your servers. They are VERY weak. kthx #OpAustralia — OperationAustralia (@Op_Australia) September 9, 2012

The attackers posted proof of their successful attacks on the websites of the AFP and the prime minister in the form of performance tests conducted by WebPagetest, a Google open-source project originally developed by America Online. The reports show that on Saturday, September 8, at 12:44 a.m. AEST (September 7 at 7:44 a.m. PT), the AFP's site was down; and on Sunday, September 9, at 1:56 a.m. AEST (September 6 at 8:56 a.m. PT), the prime minister's website was down.

Subsequent tests from users on WebPagetest show that the AFP's website returned to operation approximately three hours after the attack started. Not enough information was available to estimate how long the other sites may have been down, if at all.

All sites were running normally this morning.

The Department of Defence (DoD) told ZDNet that via the Cyber Security Operations Centre at the DSD, it is aware of "recent hacktivist group activity directed at the DSD website", but that it has experienced no technical issues and remains available. It declined to comment on any of the other websites.

This afternoon, the hackers again targeted ASIO's website, claiming to have brought it down, but the site appeared to be up at the time of writing.