People continually fall for the phone call which claims they are from Microsoft / Apple / Telstra saying there is a problem with your computer.
They then give them remote access to the computer ( would you let a stranger in the front door and go rummaging through your personal possessions ) and give them credit card details.
In a lot of cases they can access your details , clean out your bank account , gain personal information.
If you are having issues with your computer get proper help , not from someone over the phone who randomly rings you and who's credentials you cannot check.
Check out this posting from SA Police