Hp pavillion 20 that originally came with windows 8.0

Upgraded this year to windows 10

bought Webroot anti-rootkit and installed at time of purchase severall years ago.

after Webroot 2 year?? liscense expired, uninstalled it

using avast anivirus since then

Today popup asked for permission to install webroot ?? something

without thinking harder, clicked allow.

we do not have a webroot membership, or subscription.

Avast advised uninstalling second antivirus program..was not compatible with it.

uninstalled it but have no idea why it came to this computer in the first place.

want to remove all registry entries to make sure it's gone, as some reported infected unauthirized versions in internet.

Ideas??