The gunman who held hostages at a Sydney cafe made them raise a black flag widely used by jihadists.

The 16-hour siege followed months of concern over the effect on Australia's domestic security of those who fight for, or sympathise with, militant Islamist groups in Iraq and Syria.

But who are the radicalised members of Australia's Muslim community and how large is the problem?

Here's a 90-second summary.

Video produced by Michael Hirst