I had Avast for years and years, did a great job until I decided to have a 60 day free trial of their premium internet security with cleaning tools that speed up your p.c
One click and it totally destabilised my Windows, short cuts not working, would boot up and ended up paying 60 quid to put it right and in the meantime I bought a Galaxy tab 6 for use until it was returned.
The moral of the story is to either chance it and pay nowt, pay up and be sure or do what I did and f*ck it all up by having little knowledge and paying both time wise plus a hefty chunk of brass