Speaking on Channel Nine on Thursday morning, Dutton said that Australia was inundated by illegal immigrants at the time -- in 2009 -- when one of the accused suspects was thought to have arrived.

"The initial advice to me is that allegedly one of the suspects may have come to Australia with some false documentation," he said.

"At that stage, bearing in mind it was in 2009 ... Over that long period about 50,000 people came on 800 boats ...It was a difficult time for our intelligence agencies."

Abbott also acknowledged that internal threats were on the rise, and said that terror groups were "broadcasting around the world to grab a knife a flag, an iPhone and a victim".

He told Parliament on Wednesday that the rise of home grown radicals will be an ongoing problem, and that constant vigilance was required to keep the nation safe.

"This is a serious issue and I suspect it will get worse before it gets better ... there are those out there, some living in our midst, who would do us harm," Abbott said.