Terrorism threat lowered but attack 50-50

ASIO head Mike Burgess says a terrorist attack in Australia in the next 12 months remains plausible. (Mick Tsikas/AAP PHOTOS) (AAP)

Australia's terror threat has been lowered from probable to possible but security heads are warning the likelihood of an attack is 50-50.

The defeat of the Islamic State and an ineffective Al-Qaeda propaganda machine failing to connect with Western youth has resulted in fewer extremists in Australia.