Caller: supposedly, NBN

Caller (to my landline) claimed to be from NBN and said a technician would be arriving to upgrade my NBN connection ..mentioned fibre ... said they needed to perform a "Speed test" prior to the technician carrying out the work. Asked me to check the modem ...how many lights on ? Asked me to go to my computer so he could go through the steps for the 'speed test'. I said not convenient..he said he would call back next day.....He was very convincing. The "Speed test" apparently involves clicking on a link to allow access to your computer...etc etc.