The reason for Australia being apparently immune to terrorist infiltration is mainly due to their geographical location, rather than anything else. A potential terrorist has to travel thousands of miles if he has to take the sea route. Think about the size of the border that India shares with Pakistan & China, and think about the difficulties of having an outpost in such a difficult mountaineous terrain. That is why we are so vulnerable to terrorists. If someone can conduct terrorist attacks in Israel, USA & UK with their famed intelligence agencies then why not Australia ? Its simply the geography that saves Australia.