The top secret Office of National Assessments (ONA), Australia's leading intelligence assessment agency, is recruiting personnel to strengthen both its counter-terrorism branch and Open Source Centre which collects and analyses publicly available information relating to Australia's national security and international relations.

The ONA recruitment drive is at odds with the Federal Government's efforts to downside the Australian Public Service but reflects a sharp increase in resources, $630 million over four years, flowing to national security agencies in response to the perceived threat from Islamic extremists.

In an article published on Sunday Prime Minister Tony Abbott wrote that "around 60 Australians are currently fighting with terrorist groups in Iraq and Syria, with at least 100 assisting and financing their evil work."

Counter-terrorism raids in Sydney and Brisbane in the past week resulted in two arrests and saw three people detailed without charge under the Australian Security Intelligence Organisation's preventative detention powers.

The internet and social media have proved effective channels for supporters of the Islamic State (ISIL) to disseminate propaganda, attract recruits and raise funds but have also afforded Western intelligence agencies much insight into their ideological outlook, strategic intentions and support networks.

Headed by former diplomat Richard Maude, ONA is seeking analysts with a "proven record of achievement" in research relating to "foreign extremist movements, terrorism and radicalisation."

The agency is also seeking recruits to strengthen its open source collection including experts in "social media analytics, user-generated content verification, digital forensics, metadata extraction and/or web scraping", the last technique involving the use of sophisticated software to extract information from websites."

Arabic and Indonesian linguists are also being sought.

ONA's Open Source Centre, which describes itself as "an Australian eye on the world," collects and analyses publicly available information which is distributed to Australian national security agencies, other parts of government as well as allied intelligence services.

ONA defines open source information as "publicly available information regardless of the form it takes - electronic and print media, social networking sites, radio, television, databases and journals. It is anything you can read, hear or view - ranging from information carried on the latest technology through to pamphlets or flyers handed out in the street."

Open Source Centre analysts are tasked to produce "innovative analysis and research on foreign extremist groups and movements" including "individuals of security interest" "social media exploitation and quantitative analytical techniques."

US Homeland Security Secretary Jeh Johnson last week highlighted the importance of social media to the ability of ISIL and other terrorist groups to incite terrorist attacks far from conflict in Syria and Iraq.

"There is a capability to recruit people and inspire them by a terrorist organisation without them ever having to go to a terrorist camp or to get an order directly from somebody in command in a terrorist organisation right here at home," Mr Johnson told the national security conference in Maryland.

However, US intelligence officials have argued it is better to allow ISIL social media accounts to operate rather than to suppress them because of the valuable information they provide.

Beyond analysis of "open source" intelligence, US media have reported the US National Security Agency and Federal Bureau of Information have approached Facebook, Twitter and YouTube to obtain access to individual account information email addresses, contact lists and individual computer IP addresses, using that information to pinpoint the exact location of extremists.