Claiming to be from Telstra's security department, As soon as I ask what was wrong they hung up. This is most likely an attempt stating you have a virus or malware that is affecting Telstra internet infrastructure (for a small fee of course) will most likely tell you to go to a website to download the fix which in turn is more likely for them to gain remote access to your computer.

Someone keeps ringing the landline from this number about two times per day over the last year. Even weekends. Never leaving a message on answering machine. Just let them know someone is watching and they will have to explain why.