I called back number (03) 9081 1140 reached IVR for a company called Secure Australia.

I think all these numbers that start with 9081 are usually not worth picking up. I have had several missed calls from various numbers that begin with 9081 XXXX and some numbers are very similar. Strange indeed.

Google says : SECUREaustralia 2016 | Quest Events
www.questevents.com.au/secureaustralia-2016
The global security environment in rapidly evolving and has serious implications for Australian businesses, governments, infrastructure owners and areas of ...

I also have had this call twice in the past two days, mysterious!! who are they?

I called back number (03) 9081 1140 reached voice mail for a company called Secure Australia.