The worst thing is avast did not pick it up.
[b]NO[/b] security program have 100% detection or zero false positives

if it display ads it is most likely a PUP = Possible Unwated Program
https://www.virusbtn.com/resources/glossary/potentially_unwanted.xml
avast PUP detection is default off

anyway follow instructions in the guide given above and attach Malwarebytes and Farbar Recovery Scan Tool logs … 3 logs total

see below the box you write in here … Attachments and other options

removal helpers will be online later today