Have being trying to remove AVAST. But it asks for a username and password. This pair seems to be different from the one used to create an account online. I cannot remember setting one. How can either change it or remove AVAST all together without knowing that password… AVAST support provides a removal utility for a PC but not a MAC.
It’s asking for the administrator password of your Mac, so it can delete files that are not accessible for delete at the user level, it’s not related to your registration.
I will further add, that if you do not know this, boot from your OS X DVD or the recovery partition to do a reset. See here: https://support.apple.com/en-us/HT202860