Caller: Nigerian scammers

These number is used by Nigerian scammers, posed as Australian border patrol, ATO, Telstra, even Amazon. Anything that will get them to persuade me to download software from some poorly made ATO or Amazon look-alike web site. Provided that I have a hole in my head, I would then download the software and start it, following their instructions. The software will then allow them to get into my computer ad God knows what then.
Side note: They got my number after me signing up for NBN with Australian network provider called TPG. If you are customer of TPG you'll probably get a call from this number too, as TPG's database has been compromised.