I just received a call from a guy claiming to be Shaun Parker from Telstra - technical department.
He told me I had been downloading and/or uploading malicious files and that unless I cooperated with them my account would be terminated.
I didn't believe that it was a legit call so I asked for his number (03 90284553) and told him that I would call him back. I didn't call the number he gave me but called Telstra instead and explained the situation. The staff member from Telstra checked my account activity and notified me that the call definitely hadn't come from Telstra.