Canberra, Nov 28 : For the first time in almost a decade, the Australian Security and Intelligence Organisation (ASIO) on Monday officially changed the country's terrorism threat level from "probable" to "possible". It marks the first change to the level since 2014 when it was upgraded in response to the emergence of the Islamic State (IS) terror group, reports Xinhua news agency. According to Mike Burgess, the Director-General of ASIO, there have been 11 terrorist attacks in Australia since 2014 and another 21 thwarted by authorities. Of the attacks, the most notable was the 2014 Sydney hostage crisis in which three people, including perpetrator Man Haron Monis, were killed. He told reporters at ASIO headquarters in Canberra that the decision was based on a number of factors, including interviews with repatriated family members of Australian IS fighters. "A decision of this nature is not taken lightly or made casually. The process involves a large number of people and a significant amount of time," Burgess said. "Their conclusion is relatively straightforward: while Australia remains a potential terrorist target, there are fewer extremists with the intention to conduct an attack onshore than there were when we raised the threat level in 2014." ASIO's terror threat level ranges from "not expected" to "certain", with "possible" the second-lowest of the five tiers. Burgess said the most likely attack in Australia was a lone actor using a basic weapon such as a knife or vehicle. Asked about ASIO's announcement, Prime Minister Anthony Albanese said he has absolute confidence in the security agency's abilities. /IANS