Nobody will ever call you about your computer having a virus. Nobody will ever call you from "NBN Co". Nobody will ever call you from Microsoft. In fact, NOBODY WILL EVER CALL YOU ABOUT YOUR COMPUTER. If you receive any phone call about your computer or internet, IT'S A SCAM. HANG UP ON THEM. Do not open command prompt, or your web browser, don't type anything in anywhere or go to any website they tell you to go to. Hell, DON'T EVEN TURN YOUR COMPUTER ON while you're on the phone.