@ ConfusedUser

Hi and welcome to the forums.

How you managed to get avast without installing it personally is a mystery (but someone has), it is a 11MB download and the downloaded setup file has to be run and depending on your Operating System would require some user interaction, so it isn’t something that can be installed by accident.

You are however fortunate to have it as it is a very good Anti-Virus as many reviews and comparative sites attest. I have had it installed for nearly three years without serious issues and I find it the most configurable and flexible AV I have used and I have tried a few ;D

Probably more important do (or did) you have another AV installed on this system (as two might conflict) ?