I've been bugged

I found this insect wandering around an Elk-horn Fern (Platycerium bifurcatum) in the garden. It's about 25 mm long. I reckon it's a bug, and probably a Shield or Stink Bug. This one on the Brisbane Insects website, the Acacia Shield Bug, looks close. But there are many species. 

This bug may have originated in Canberra. The particular Elk-horn it was found in (see extra) came from Canberra last week. The plant was in our Canberra garden for all our time living there. When we moved out 2 years ago we left it with a friend. When we returned from our recent visit to Canberra we had room in the car to bring the Elk-horn back to Lennox Head. And maybe the bug also. I wonder what else we brought?